CHAPTER XXVII

.

GENERA OF PTERIDOSPERMS, FERNS, AND _PLANTAE INCERTAE SEDIS._

The genera and species described in this Chapter are founded on sterile leaves or portions of leaves, and in the great majority of cases the reproductive organs are either imperfectly known or have still to be discovered. Some of the genera, the smaller number, are no doubt true ferns, while most of them may safely be regarded as plants which will ultimately be shown to belong to some other group, in most cases that of the Pteridosperms. It is possible that a few of the types may be members of the Cycadophyta rather than of the Pteridospermeae, but evidence as to systematic position is for the most part of a negative kind or too incomplete to lead to any definite expression of opinion as to the cycadean or pteridosperm nature of the imperfectly known Palaeozoic or Mesozoic species. Many of the genera are of little botanical interest, though even the most problematical are of importance as criteria of geological age. Genera which there is good reason for including in the Pteridosperms are dealt with in this section, in order that the Chapter in Volume III. devoted to this important group may be limited to more completely known types.

In most text-books it is customary to employ family names for sterile fern-like fronds which possess similar venation features or have in common certain vegetative characters, the value of which it is impossible to estimate. In the following account family or group names are not adopted, on the ground that such slight utility as they may have is more than counterbalanced by the risk attending a grouping under one name of plants which may agree only in unessential characters. The practice of classifying fossil plants has been carried to excess. Grouping together genera as a matter of convenience unavoidably creates a prejudice in favour of actual relationship, which may or may not exist.

Taeniopteris.

This generic name was instituted by Brongniart[1254] for simple linear or broadly linear leaves with a prominent midrib from which secondary veins, simple or dichotomously branched, are given off at right angles or obliquely. The frond of the type-species _Taeniopteris vittata_ (fig. 332), characteristic of Jurassic floras, was compared by Brongniart with the pinnules of _Danaea_ and _Angiopteris_. Among recent ferns the Taeniopteris form of frond and venation is represented by _Oleandra neriiformis_, _Asplenium nidus_, and many other species. Though usually applied to fronds which there is good reason for regarding as simple leaves, the generic designation _Taeniopteris_ has been extended to include pinnate fronds, e.g. the Upper Palaeozoic species _T. jejunata_ Grand’Eury, and _T. Carnoti_ Ren. and Zeill. (fig. 330, A). The compound fronds from the Lower Coal-Measures of Missouri described by Dr White[1255] as _T. missouriensis_ are characterised by decurrent and confluent Taeniopteroid pinnules. In a later reference[1256] to this plant White pertinently adds, “perhaps it belongs more properly in _Alethopteris_.”

Leaves of the _Taeniopteris_ type are described by several authors as species of _Oleandridium_, _Angiopteridium_, _Danaeites_, _Marattia_, and other genera. In such species of Taeniopteroid leaves as have been dealt with in a former Chapter, the occurrence of sori justifies the substitution of a name denoting a close relationship to existing members of the Marattiaceae, but in the absence of fertile specimens the provisional designation _Taeniopteris_ should be retained. It is often difficult to decide between _Taeniopteris_ and _Nilssonia_ as the more suitable name to apply to fragments of fossil leaves of Mesozoic age. _Taeniopteris_ is, however, distinguished from the Cycadean genus by the greater prominence of the rachis, also by the dichotomous branching of the secondary veins, usually close to their origin and at varying distances between the axis of the frond and the edge of the lamina. The genus _Taeniopteris_, though most abundant in Rhaetic and Jurassic strata, occurs also in Upper Carboniferous and Lower Permian rocks. The generic name _Macrotaeniopteris_ instituted by Schimper[1257] has been used for leaves differing only in size from the usual type of _Taeniopteris_, but there is no adequate reason for its retention.

The species included in _Taeniopteris_ afford no satisfactory evidence as to their systematic position. It is obviously unwise to adopt such generic titles as _Oleandridium_, _Marattiopsis_, etc., merely because of resemblance in the venation of sterile fragments to _Oleandra_ or Marattiaceous ferns.

Some specimens of _Taeniopteris_ fronds described by Mr Sellards[1258] from Permian rocks of Kansas, which are referred to later, have furnished unconvincing evidence of reproductive organs.

_Taeniopteris multinervis_, Weiss. Fig. 329, A, B.

The late Dr Weiss[1259] instituted this species (which he designated _Taeniopteris multinervia_, though the specific name _multinervis_ is constantly used) for a fragment of a leaf from the Lower Permian of Lebach characterised by numerous forked veins given off at right angles from a prominent rachis (fig. 329, B). This type of frond is recorded from the Permian of Trienbach (Alsace) by Zeiller[1260], by Renault[1261] and Zeiller[1262] from the Upper Carboniferous of Autun, and from other localities. The lamina of the simple leaf reaches a breadth of 6 cm. and a length of 40 cm. (fig. 329, A); the numerous secondary veins (25–36 per cm. of lamina) are either at right angles to the rachis or given off at an acute angle. The mesophyll consists of polygonal cells some of which are elongated at right angles to the surface of the lamina. A very similar form is described by Fontaine and White from the Permian of Virginia as _T. Lescuriana_[1263].

[Illustration: FIG. 329.

A. _Taeniopteris multinervis_, Weiss. (⅚ nat. size. After Zeiller.) B. _T. multinervis._ (Enlarged. After Zeiller.) C. _Lesleya Delafondi._ (× 2. After Zeiller.)]

It is futile to expect to be able to separate the numerous _Taeniopteris_ leaves into well-defined species: all we can do is to group the specimens under different names, using as artificial distinctions such characters as the shape of the leaf, the number of veins per centimetre, and the prominence of the rachis. Another Virginian species of Permian age described by Fontaine and White[1264], _T. Newberriana_, is said to bear sori, but no satisfactory information is given as to the nature of these organs. Specimens referred with some hesitation to this species and to a similar species, _T. coriacea_, have been described by Sellards[1265] from material obtained from Permian beds in Kansas. The lamina of the simple linear fronds is characterised by the occurrence of small oval bodies half immersed in the substance of the leaf between the secondary veins (figs. 330, D, E). One of these bodies is represented in an apparently dehisced condition in fig. 330, D. Sellards suggests the possibility that these bodies are sporangia, but, as he points out, they afford no indication of cellular structure nor are they in direct connexion with the veins.

_Taeniopteris jejunata_, Grand’Eury[1266].

This species differs from _T. multinervis_ in its bipinnate fronds; the linear or oval-linear pinnae are attached by a short stalk to the primary rachis and reach a length of 25 cm.; the veins are less crowded, 12–15 per centimetre.

_T. jejunata_ is recorded from the Coal-fields of the Loire and Commentry[1267] in France, from the Lower Permian of Thuringia[1268], and elsewhere.

_Taeniopteris Carnoti_, Ren. and Zeiller[1269]. Fig. 330, A.

This species, founded on portions of pinnate fronds from the Coal-field of Commentry, is characterised by rather broader (25–30 mm.) pinnules, with short pedicels and a cordate base, reaching a length of 25–30 cm. The secondary forked veins are more numerous than in _T. jejunata_. In _T. multinervis_ the pinnules are still broader and have a stronger midrib.

• • • • •

Several species of _Taeniopteris_ have been described from Triasso-Rhaetic rocks in Europe, India, Tonkin and elsewhere. In some cases it is practically impossible to recognise clear specific distinctions between Rhaetic and Jurassic types.

From the Damuda and Panchet series of India (Triasso-Rhaetic) Feistmantel has described large sterile fronds as _Macrotaeniopteris Feddeni_[1270] which reach a breadth of 20 cm.: these may be compared with the Indian species _Taeniopteris lata_ Oldham[1271], and to _T. gigantea_ from the Rhaetic of Franconia[1272] and Scania. A specimen of this species figured by Nathorst[1273] from Scania has a lamina 33 cm. broad. Other examples are afforded by _M. Wianamattae_ Feist.[1274] from rocks of the same age in Australia and by _Taeniopteris superba_ Sap.[1275] from Lower Rhaetic rocks near Autun.

From the Rhaetic of Tonkin, Zeiller records several species, among which may be mentioned _T. Jourdyi_ Zeill.[1276] and _T. spatulata_ MacClelland (fig. 330, B, C). Both have simple fronds. Those of _T. Jourdyi_ reach a length of 10–40 cm. and a breadth of 10–70 mm.; the rachis is characterised by crowded and discontinuous transverse folds, and the secondary veins (35–50 per cm.) are usually at right angles to the rachis. This Tonkin species is compared by Zeiller with the European Rhaetic species _T. tenuinervis_ Brauns.

The polymorphism of the fronds is a striking feature: in one case described by Zeiller the lamina appears to be divided into segments like those characteristic of the leaf of the Cycadean genus _Anomozamites_. It is obviously difficult in many instances to distinguish between detached Taeniopteroid pinnae of a compound frond and complete simple leaves. In some compound fern fronds, as in the recent Polypodiaceous genus _Didymochlaena_, the pinnules are deciduous, and the same feature undoubtedly characterised the fronds of many extinct species. A specimen figured by Zeiller which shows several petioles of _T. Jourdyi_ attached to a thick stem[1277] demonstrates the simple nature of the leaves. In other cases, e.g. _T. vittata_, specimens occur in which the slightly enlarged petiole-base has a clean-cut surface indicating abscission from a rhizome (fig. 332).

The fronds described by Zeiller as _T. spatulata_[1278] (fig. 330, B, C) closely resemble Jurassic leaves from Victoria referred to _Taeniopteris Daintreei_ McCoy[1279].

[Illustration: FIG. 330.

A. _Taeniopteris Carnoti_, Ren. and Zeill. (Nat. size. After Renault and Zeiller.) B. _T. spatulata_, McClell. (Nat. size. After Zeiller.) C. _T. spatulata._ (× 3. After Zeiller.) D. Supposed sporangium of _T. coriacea._ (× 15. After Sellards.) E. _T. coriacea._ (× 2. After Sellards.)]

Whether specifically identical or not, these leaves represent a type distinguished from the other species of the genus by the small breadth of the linear-lanceolate or linear-spathulate lamina, which may be 6–15 cm. in length and 3–12 mm. broad. The lamina is often characterised by transverse folds (fig. 330, C).

_Taeniopteris Carruthersi._ Fig. 331.

1872. _Taeniopteris Daintreei_, Carruthers, Quart. Journ. Geol. Soc. Vol. XXVIII. Pl. XXVII. fig. 6.

1883. _T. Carruthersi_, Tenison-Woods, Proc. Linn. Soc. N. S. Wales, Vol. VIII. p. 117.

[Illustration: FIG. 331. _Taeniopteris Carruthersi_, Ten.-Woods. Nat. size.]

The simple fronds included under this specific name are characterised by a strong midrib from which numerous simple or forked secondary veins are given off at a right angle or slightly inclined. The breadth of the lamina decreases gradually towards the petiole. The Australian species named by McCoy _Taeniopteris Daintreei_, to which Carruthers referred the Queensland fossils, has a much narrower and more linear form of frond, and for this reason Tenison-Woods instituted a new specific name. _T. Carruthersi_ represents a form of leaf met with in Rhaetic, or possibly Upper Triassic, rocks in S. Africa[1280] and Australia. A very similar, perhaps an identical type, was described from Argentina by Geinitz[1281] as _T. mareyiaca_: among many other examples of this form of frond may be mentioned _T. immersa_[1282] Nath. from the Rhaetic rocks of Scania and _T. virgulata_ from the Rhaetic of Tonkin[1283].

A comparison of _Taeniopteris Carruthersi_ or various other “species” of Rhaetic fronds with the Jurassic species _T. vittata_ illustrates the slight and unimportant differences on which specific separation is based. It is hopeless to attempt to draw a satisfactory distinction between the numerous Taeniopteris fronds from Upper Triassic and Jurassic rocks.

_Taeniopteris vittata_, Brongniart. Fig. 332.

The simple leaves to which Brongniart applied this name are characteristic of the Inferior Oolite flora of England, and examples of the same type are recorded from Jurassic rocks of India, Poland, the Arctic regions, Japan, China, Australia and other countries[1284].

Leaf linear-lanceolate, reaching a length of more than 20 cm. and a breadth of 3 cm. The lamina increases gradually in breadth from the base and tapers towards the apex. Numerous secondary veins are given off at right angles from a broad midrib: the lateral veins may be simple or forked close to their origin, near the margin, or in the intermediate portion, of the lamina.

It is exceedingly difficult to use _Taeniopteris_ leaves of this form as evidence in regard to the Jurassic or Rhaetic age of plant-bearing strata. The species _T. tenuinervis_ Brauns, as figured by Schenk[1285] from the Rhaetic rocks of Germany and Persia, and recorded from several other regions, presents a close agreement with _T. vittata_. _Oleandridium lentriculiforme_ Etheridge[1286] from the Hawkesbury series of Australia is another similar leaf. The species _T. vittata_ from the Yorkshire coast, represented in fig. 332, shows a well-preserved petiole with a clean-cut base like that of the petioles of _Oleandra neriiformis_ and other recent ferns which are detached from the rhizome by the action of an absciss-layer.

[Illustration: FIG. 332. _Taeniopteris vittata._ (British Museum No. 39217. ⅔ nat. size.)]

A broader form of frond with similar venation was described by Lindley and Hutton[1287] as _Taeniopteris major_. An examination of the type-specimen from the Inferior Oolite of Yorkshire, now in the Manchester Museum, led me to doubt the necessity of specific separation from _T. vittata_[1288].

A smaller frond of the same general type as _T. vittata_ is recorded from Wealden strata of North Germany and England under the name _T. Beyrichii_[1289].

Weichselia.

This generic name was instituted by Stiehler[1290] for impressions of bipinnate sterile fronds, presumably ferns, from Lower Cretaceous rocks near Quedlinburg. The same type of leaf from English Wealden beds had previously been referred by Mantell and other authors to _Pecopteris_, and by Brongniart to his genus _Lonchopteris_[1291]. It is, however, advisable to follow Nathorst’s example[1292] and restrict the latter name to Palaeozoic species. As already suggested, it would obviate confusion to substitute a new generic designation for _Lonchopteris_ in the case of Triassic species which are probably members of the Osmundaceae. The type-species of Stiehler, _Weichselia Ludowicae_[1293], does not differ in any important character from _Weichselia Mantelli_, the species originally described by Stokes and Webb from the Wealden of England as _Pecopteris reticulata_.

_Weichselia Mantelli_ (Brongn.)[1294]. Fig. 333.

1824. _Pecopteris reticulata_, Stokes and Webb, Trans. Geol. Soc. [2]. Vol. I. p. 423, Pls. XLVI. XLVII.

1828. _Lonchopteris Mantelli_, Brongniart, Prod. p. 6; Hist. vég. foss. p. 369, Pl. CXXXI.

1894. _Weichselia Mantelli_, Seward, Wealden Flora, Vol. I. p. 114. Pl. X. fig. 3.

1899. _Weichselia reticulata_, Fontaine, in Ward, Ann. Rep. U. S. Geol. Surv. p. 651.

Frond bipinnate, rachis broad; pinnae very long, of uniform breadth and with prominent axes; pinnules crowded, entire, with obtuse apex, usually oblong but more or less triangular or rounded towards the distal ends of the pinnae. The pinnules, which may reach a length of 9 cm., are characterised by a fleshy lamina attached by the whole breadth of the base; the two rows of segments on each secondary rachis are usually inclined towards one another so that they form with the axis of the pinna a wide-open =V= instead of lying in one plane (fig. 333, C). From a median rib are given off numerous anastomosing branches (fig. 333, B).

[Illustration: FIG. 333. _Weichselia Mantelli._

A. Part of a frond from the Wealden of Sussex, England. (British Museum; v. 2630. ¾ nat. size.) B. Pinnule from Bernissart, Belgium (× 3). C. _Weichselia erratica_, Nath. Section of pinna. (After Nathorst.)]

This characteristic Wealden species is recorded from England, Germany, France, Belgium, Austria, Russia, Bornholm, North America, and Japan. It is by no means certain that _Weichselia Mantelli_ is a true fern: no satisfactory evidence of fructification has been adduced.

The broad and strong rachis is comparable with that of a Cycadean leaf and the thick lamina suggests a plant of xerophilous habit. I have retained the specific name _Mantelli_ on the ground of long established usage instead of following Fontaine in his adherence to strict priority.

Glossopteris.

The name _Glossopteris_ was proposed by Brongniart in 1822[1295] for an imperfect leaf-impression which he called _Filicites_ (_Glossopteris_) _dubius_, but the specimen so named has since been identified as part of a sporophyll of a _Lepidostrobus_. The author of the genus afterwards published[1296] a diagnosis, based on well-preserved leaves from Permo-Carboniferous rocks in Australia and India, of the type-species _Glossopteris Browniana_, the Indian examples being distinguished as _G. Browniana_ var. _indica_ while the Australian form was named _G. Browniana_ var. _australasica_. Schimper[1297] afterwards raised the Indian fossils to specific rank as _G. indica_ though some authors[1298] have continued to consider the two forms as insufficiently distinct to be regarded as different species.

The genus _Glossopteris_ may be defined as follows:

Leaves simple, varying considerably in size, shape, and venation characters, but almost without exception characterised by repeatedly anastomosing lateral veins. The leaves are of two kinds: (i) _foliage leaves_; apparently always sterile, usually spathulate, with an obtuse apex, a well-marked midrib which may persist to the apex or die out in the upper half of the lamina, characterised by its slight prominence and comparatively great breadth especially in the basal part of the frond. In most cases the lamina extends as a narrow margin to the leaf-base, but in a few forms there is a short petiole (fig. 334). Though usually spathulate, the frond may be linear-lanceolate, or ovate; the apex is sometimes acute. Leaves vary in length from 3 to 40 cm. and may in larger forms have a breadth of 10 cm. Numerous lateral veins curve upwards and outwards to the margin of the lamina or pursue a straight course almost at right-angles to the midrib. (ii) _Scale-leaves_[1299] which differ from the foliage-leaves in their much smaller size and in the absence of a midrib; they are deltoid, oval or cordate in shape and generally terminate in an acute apex; the edge of the lamina may be slightly incurved so that the leaf presents a convex upper surface supplied with anastomosing veins. The scale-leaves, which vary in length from about 1 to 6 cm., probably acted as sporophylls. The only evidence as to the nature of the fructification so far obtained is represented by empty sporangium-like organs (1·2–1·5 mm. long by 0·6–0·8 mm. broad) frequently associated with the scale-leaves[1300].

The leaves, in some cases at least, were borne near together on a cylindrical stem or rhizome which produced branched adventitious roots[1301]. The fossils long known as _Vertebraria_ were recognised by Zeiller[1302] and by Oldham[1303] as the stems of _Glossopteris_.

The systematic position of _Glossopteris_ must for the present be left an open question. Though usually spoken of as a fern, it is noteworthy that despite the enormous abundance of its foliage leaves in the Permo-Carboniferous strata of India, Australia, South Africa, and South America, no single example has been discovered which shows undoubted remains of sori or sporangia. Many authors have described fertile leaves of _Glossopteris_; but it was not until Arber’s discovery of sporangia in close association with the scale-leaves that any light was thrown on the nature of the reproductive organs.

The probability is that _Glossopteris_ was not a true fern but a member of that large and ever-increasing class, the Pteridosperms. This opinion is based largely on negative evidence. Such sporangia as have been described may have contained microspores and the plant may have been heterosporous. The occurrence of seeds in association with Glossopteris fronds recorded by more than one writer[1304], though by no means decisive and possibly the result of chance association, is favourable to this view. Dr White[1305] has suggested that the small leaves described by Zeiller[1306] as _Ottokaria bengalensis_ from Lower Gondwana (Permo-Carboniferous) rocks of India, and similar fossils recorded by himself from Brazil as _O. ovalis_, may represent “sporangiferous” organs of _Glossopteris_ or _Gangamopteris_, “both of which are probably pteridospermic.” There is, however, no conclusive evidence in support of this suggestion.

The genus, whatever its position may be, has a special interest for the geologist and for the student of plant distribution; it is a characteristic member of a Permo-Carboniferous flora which flourished over an enormous area, including India, South Africa,—extending from Cape Colony to Rhodesia and German East Africa[1307],—Australia, and South America[1308]. This flora, known as the Glossopteris flora, differed considerably in its component genera from that which overspread Europe and North America and some more southern regions in the Upper Carboniferous and Permian periods.

The discovery by Amalitzky[1309] of _Glossopteris_, and other genera characteristic of the Glossopteris flora, in the Upper Permian rocks in Vologda (Russia) demonstrates the existence of a northern outpost of the southern botanical province, and Zeiller’s discovery of the genus in the Rhaetic flora of Tonkin[1310] shows that _Glossopteris_ persisted beyond the limits of the Palaeozoic epoch. Dr David White[1311] has recently proposed to re-christen the Glossopteris flora the Gangamopteris flora on the ground that _Gangamopteris_ is strictly Palaeozoic in its range, whereas _Glossopteris_ persisted into the Mesozoic era; this is perhaps hardly a sufficient reason for giving up so well established a title as the Glossopteris flora. A fuller account of this southern flora must be reserved for another volume.

_Glossopteris Browniana_, Brongniart[1312]. Figs. 334–36.

The specific name _Browniana_ is now applied to obtusely pointed leaves which sometimes reach a length of 15 cm., but are usually rather shorter. In form and venation they closely resemble the leaves of the recent genus _Antrophyum_ and species of _Acrostichum_. The comparatively broad midrib may be replaced in its proximal portion by several parallel veins: from it are given off numerous lateral veins which form a reticulum characterised by meshes approximately equal in size and elongated in a direction parallel to the general course of the secondary veins (fig. 334).

[Illustration: FIG. 334. _Glossopteris Browniana_, Brongn. A. Nat. size: B × 3½.]

The drawings, originally published by Zeiller[1313], reproduced in fig. 335 illustrate the venation and its range of variation; the meshes are usually hexagonal and arranged as shown in figs. A and B, but occasionally (fig. 335, C) they follow a more steeply inclined course.

Small leaves with a more or less distinct midrib, 2–3 cm. in length, supply transitional stages between foliage- and scale-leaves. In the true scale-leaves spreading and occasionally anastomosing veins take the place of the midrib and lateral veins of the ordinary frond. McCoy[1314] in describing some Australian specimens of _Glossopteris_ in 1847 spoke of scale-like appendages of the rhizome which he compared with the large ramenta of _Acrostichum_ and other ferns. It was, however, Zeiller[1315] who first recognised the leaf-nature of these scales and adequately described them; additional figures of scale-leaves have been published by Mr Arber[1316] and by myself[1317]. The importance of these small leaves has been considerably increased by Mr Arber’s discovery of associated sporangia which, as he suggests, were probably borne on their lower concave surface.

[Illustration: FIG. 335. _Glossopteris Browniana_, Brongn. (After Zeiller. × 2.)]

The sporangia (fig. 336) are compared by Arber with the microsporangia of recent Cycads and with the Palaeozoic sporangia described by Zeiller as _Discopteris Rallii_ (fig. 256, D); the latter are distinguished by the well-defined group of thicker walled cells representing the annulus of true fern sporangia. We know nothing as to the contents of the Glossopteris sporangia, whether they contained microspores or whether they are the spore-capsules of a homosporous plant.

[Illustration: FIG. 336. _Glossopteris Browniana_, Brongn. Sporangia. (× 30). After Arber.]

The rhizome of _Glossopteris Browniana_ has been described in detail by Zeiller, who first demonstrated that the fossils originally assigned by Royle[1318] to the genus _Vertebraria_ represent the stem of this and, as we now know, of some other species of _Glossopteris_. _Vertebraria_ occurs in abundance in Permo-Carboniferous strata in association with _Glossopteris_; the differences between Australian, Indian, and South forms, though expressed by specific names, are insignificant. The stems are usually preserved in the form of flattened, single or branched, axes sometimes bearing slender branched roots and characterised by one or two, or less frequently three, longitudinal grooves or ridges (fig. 337) from which lateral grooves or ridges are given off at right angles, dividing the surface into more or less rectangular areas 1 cm. or more in length. The surface of these areas is often slightly convex and in some specimens the outlines of cells may be detected. Mr Oldham has described some interesting examples of _Vertebraria_ from India in which the longitudinal and transverse grooves are occupied by a dark brown ferruginous substance or by the carbonised remains of plant-tissues (fig. 338, C, D). In transverse section, a _Vertebraria_ cast appears to be divided into a number of wedge-shaped segments radiating from a common centre. Prof. Zeiller[1319] has figured specimens of _Vertebraria_ with portions of Glossopteris fronds still attached.

[Illustration: FIG. 337. _Vertebraria indica_, Royle. Nat. size. (After Feistmantel.)]

The rhizome of _Glossopteris_, as represented by the Vertebraria casts, is aptly compared by Zeiller[1320] with that of the recent Polypodiaceous fern _Onoclea struthiopteris_. Sections of the recent stem (fig. 338, E, F) show that the form is irregularly stellate owing to the presence of prominent wings which anastomose laterally at intervals as shown by the examination of a series of sections. The leaf-traces are derived from the steles of adjacent wings. Fig. 338 (B and A) represents somewhat diagrammatically a longitudinal and transverse view of a _Vertebraria_; the radiating arms represented in the transverse section (fig. A) are the stem ribs or wings and the segments between them are intrusions of sedimentary material. The rectangular areas characteristic of the surface of a _Vertebraria_ are the intruded segments of rock: these are separated at intervals by transverse grooves, which mark the course of vascular strands given off at each anastomosis of the longitudinal wings to supply the leaves.

[Illustration: FIG. 338.

A, B. _Vertebraria indica._ (After Zeiller.) C, D. _V. indica._ (Nat. size. After Oldham.) E, F. _Onoclea struthiopteris._ (× 2. After Zeiller.)]

Mr Oldham, who discovered the connexion between _Glossopteris_ and _Vertebraria_ independently of Dr Zeiller, does not agree with the interpretation of the structural features of the rhizome which Zeiller bases on a comparison between Vertebraria and _Onoclea struthiopteris_. Oldham[1321] describes _Vertebraria_ as consisting of a central axis “joined to an outer rind by a series of radial septa,” the spaces between the septa being divided into chambers by transverse partitions. His view is that the rhizome of _Glossopteris_ was a cylindrical organ and not an irregularly winged axis like the stem of _Onoclea_. Zeiller[1322] has replied in detail to Oldham’s interpretation and adheres to his original view, that the rhizome consisted of a solid axis with radial wings or flanges which at intervals anastomosed transversely in pairs at the nodes. It may, however, be possible that the spaces between the longitudinal and transverse grooves on a Vertebraria axis, which have been filled with the surrounding rock, were originally occupied in part at least by secondary wood, and the transverse strips of carbonaceous material[1323] lying in the grooves may represent medullary-ray tissue and accompanying leaf-traces. The longitudinal striations seen in some specimens of _Vertebraria_ on the areas between the grooves may be the impressions of woody tissue. It is impossible without the aid of more perfectly preserved material to arrive at a satisfactory conception of the structural features of a complete Glossopteris rhizome.

[Illustration: FIG. 339. _Glossopteris_ fronds attached to rhizome. (From a specimen lent by Dr Mohlengraaff. Considerably reduced.)]

In the specimen of _Glossopteris Browniana_ shown in fig. 339 several leaves are attached to an axis which shows none of the surface-features of _Vertebraria_. I am indebted to the kindness of Dr Mohlengraaff of Delft for the loan of this specimen which was obtained from Permo-Carboniferous rocks in the Transvaal. An axis figured by Etheridge[1324] from an Australian locality bears a tuft of _Glossopteris_ leaves, possibly _G. Browniana_; in place of the rectangular areas characteristic of _Vertebraria_ it shows transversely elongated leaf-scars or, on the internal cast, imbricate rod-like projections which Etheridge suggests represent vascular bundles.

_Glossopteris indica_, Schimper. Figs. 340, A, 341.

It is a question of secondary importance whether or not the fronds which Brongniart spoke of as a variety of _Glossopteris Browniana_ should be recognised as specifically distinct. The careful examination by Zeiller of the venation characters has, however, afforded justification for separating _G. Browniana_ and _G. indica_. We must admit that the slight and not very constant differences in the size and form of the meshes produced by the anastomosing of the lateral veins are characters which cannot be recognised as having more than a secondary value, though, as a matter of convenience, we employ them as aids to determination. The arbitrary separation of sterile leaves, which differ by small degrees from one another in form and in the details of venation, by the application of specific names is a thankless task necessitated by custom and convenience; it is, however, idle to ignore the artificial basis of such separation. Mr Arber has recently published, in his valuable _Glossopteris Flora_, an analytical key which serves to facilitate the description and determination of different types of frond[1325].

[Illustration: FIG. 340.

A. _Glossopteris indica_, Schimper. (½ nat. size.) B. _Glossopteris angustifolia_, Brongniart. (Nat. size.) From Arber, after Feistmantel.]

The large leaves of _Glossopteris indica_, reaching a length in extreme cases of 40 cm. and a breadth of 10 cm., are characterised by a rather greater regularity in the arrangement of the meshes and by the greater parallelism of the upper and lower sides of each mesh (fig. 341) and by less difference in size between the venation meshes than in _G. Browniana_, the leaves of which are usually smaller. The relatively thick epidermis consists of rectangular cells with stomata in depressions[1326]. The scale-leaves[1327], rather larger than those of _G. Browniana_, are more or less rhomboidal with rounded angles and reach a length of 1·5–6 cm. and a breadth of 1·5–2·5 cm. The rhizome is practically identical with that of _G. Browniana_[1328].

[Illustration: FIG. 341. _Glossopteris indica_, Schimp. (× 1½.) From Arber, after Zeiller.]

This species occurs in great abundance in the Permo-Carboniferous rocks of India, Australia, and in various parts of South Africa, and elsewhere. It has been recognised also by Amalitzky[1329] in Upper Permian beds in Russia and by Zeiller in the Rhaetic series of Tonkin[1330].

[Illustration: FIG. 342. _Glossopteris angustifolia_ var. _taeniopteroides_. (× 3½.)]

_Glossopteris angustifolia_, Brongniart. Figs. 340, B; 342.

It is convenient to retain this designation for linear fronds with an acute or obtuse apex and a venation-reticulum composed of long and narrow meshes (fig. 340, B). It is by no means unlikely, as Arber suggests, that the same plant may have produced leaves of the _G. indica_ type and narrower fronds which conform to _G. angustifolia_. In his description of some Indian specimens of _G. indica_, Zeiller draws attention to the variation exhibited in regard to the extent of anastomosing between the secondary veins: some examples with very few cross-connexions agree more closely with _Taeniopteris_ than with _Glossopteris_ as usually defined[1331]. The venation shown in fig. 342 illustrates an extreme case of what is almost certainly a Glossopteris leaf of the _G. angustifolia_ type. This specimen, which was discovered by Mr Leslie in the Permo-Carboniferous sandstone of Vereeniging (Transvaal), has been referred to a variety of Brongniart’s species as _G. angustifolia_ var. _taeniopteroides_[1332] on account of the almost complete absence of any cross-connexions. The reference to _Glossopteris_, which my friend Dr Zeiller suggested, is amply justified by the form of the leaf as a whole, by the angle at which the lateral veins leave the midrib, a feature in contrast to the wider angle at which the lateral veins are usually given off in _Taeniopteris_ (figs. 329, 332), and by the similarity to the Indian specimens already mentioned. Several authors have described leaves or leaflets under the generic name _Megalopteris_[1333] from Carboniferous and Permian rocks which bear a close resemblance to the South African variety, but in some cases at least _Megalopteris_ is known to be a pinnate and not a simple leaf. The leaf figured by Jack and Etheridge as _Taeniopteris_ sp.[1334] from Queensland may also be an example of _Glossopteris_. Comparison may be made also with the Palaeozoic leaves described in the first instance by Lesquereux and more recently by Renault and Zeiller as species of _Lesleya_[1335] (fig. 347).

[Illustration: FIG. 343. _Blechnoxylon talbragarense_, Eth.: _s_, scale-leaves; _x_, secondary xylem. (After Etheridge. A × 2; B × 3; C much enlarged.)]

_Blechnoxylon talbragarense_, Etheridge. Fig. 343.

Under this name Etheridge[1336] described some specimens from the Permo-Carboniferous Coal-Measures of New South Wales, which he regards as a fern, comparable, in the possession of a cylinder of secondary xylem, with the recent genus _Botrychium_ and with _Lyginodendron_ and other members of the Cycadofilices. The slender axis (1–3 mm. in diameter) appears to consist of a zone of radially disposed tissue (fig. 343, C, _x_), which is probably of the nature of secondary xylem, enclosing a pith and surrounded externally by imperfectly preserved remnants of cortex. Unfortunately no anatomical details could be made out, but the general appearance, if not due to inorganic structure, certainly supports Etheridge’s determination. The stem bore at intervals clusters of linear-lanceolate leaves (reaching 12 mm. in length) in close spirals (fig. 343, A and B); the leaves are characterised by a strong midrib and forked secondary veins. Small “pyriform” bodies of the nature of scale-leaves occur in association with the fronds (fig. 343, B, _s_).

In his description of this interesting plant, Etheridge quotes an opinion which I expressed in regard to the comparison of the stem with those of _Botrychium_, _Lyginodendron_, and other genera. No satisfactory evidence has been found as to the nature of the fructification. Although the leaves of _Blechnoxylon_ are much smaller than those of _Glossopteris_, I am now disposed to regard the genus as closely allied or even generically referable to _Glossopteris_. The crowded disposition of the leaves is like that in _Glossopteris_, shown in fig. 339 and in the figures published by Etheridge and by Oldham; the association of scale-leaves and foliage-leaves is another feature in common. The absence of a reticulum of anastomosing veins can no longer be considered a fatal objection to the suggestion that the Australian type may be a species of _Glossopteris_. If the view that _Blechnoxylon_ is not a distinct genus is correct, the occurrence of secondary xylem is favourable to the opinion already expressed that _Glossopteris_ is more likely to be a Pteridosperm than a true fern. The data at present available render it advisable to retain Mr Etheridge’s name: the comparison with _Glossopteris_ lacks confirmation.

[Sidenote: BLECHNOXYLON]

[Illustration: FIG. 344. _Glossopteris retifera._ (Nat. size. From Arber, after Feistmantel.)]

_Glossopteris retifera_, Feist. Fig. 344.

In some _Glossopteris_ leaves the anastomosing secondary veins form a coarser reticulum, as in the example represented in fig. 344. The name _G. retifera_ was given by Feistmantel[1337] to Indian fronds of this type; similar forms have been described as _G. conspicua_ and _G. Tatei_. The type illustrated by _G. retifera_ is recorded also from Permo-Carboniferous rocks in Zululand[1338], Natal, the Transvaal, Cape Colony, and the Argentine.

Gangamopteris.

In 1847 McCoy[1339] described a leaf-fragment from Permo-Carboniferous rocks in New South Wales as _Cyclopteris angustifolia_. The type-specimen of this species, which is now in the Sedgwick Museum, Cambridge, has been re-described by Mr Arber[1340]. Subsequently[1341] McCoy instituted the generic name _Gangamopteris_ for leaves, like that previously referred by him to _Cyclopteris_, from the Bacchus Marsh Sandstone, of New South Wales, but he did not publish a diagnosis of the genus until several years later[1342]. Feistmantel[1343], who has described many species of _Gangamopteris_ from the Lower Gondwana strata of India, slightly modified the original diagnosis. The genus is represented by sterile fronds only. We know nothing of the stem, and such evidence as is available in regard to the form of the fertile leaves is of a circumstantial kind. It is, however, highly probable that _Gangamopteris_ is not a true fern but a Pteridosperm.

Leaves simple, sessile, varying in shape; obovate or spathulate, broadly lanceolate or rarely linear; the apex is usually blunt (fig. 345) but occasionally gradually tapered. In general appearance a Gangamopteris leaf is similar to that of _Glossopteris indica_, the chief distinction being the absence of a midrib. Gangamopteris leaves are on the whole larger than those of _Glossopteris_; many of them reach a length of 20 cm. and some of the large Indian fronds are nearly 40 cm. long. The venation of _Gangamopteris_ shows a greater uniformity in the size and shape of the meshes than that of _Glossopteris_. The middle of the lamina, especially in the lower part, is occupied by a few vertical veins from which branches curve upwards and outwards towards the edge of the lamina. The secondary veins are connected by frequent anastomoses and agree very closely with those of _Glossopteris_. The lamina becomes narrower towards the base, which is either cuneate or in some cases slightly auriculate (fig. 345).

As I have elsewhere pointed out[1344], the presence or absence of a midrib is not in itself a character of real taxonomic importance. In the recent fern _Scolopendrium vulgare_ the frond has a prominent midrib, while in _S. nigripes_ there is no median rib. Mr Arber has expressed the opinion that “it is extremely doubtful whether the genus _Gangamopteris_ should not be merged in _Glossopteris_[1345].” The retention of the two names is, however, convenient, and it would tend to confusion were we to carry to its logical conclusion the view that the recognised distinction between the two genera may not be a mark of generic difference.

_Gangamopteris_ is confined to Palaeozoic strata, a fact which leads White[1346] to speak of the Gangamopteris rather than of the Glossopteris Flora. It occurs in South America, South Africa, Australia, and India, extending as far north as Kashmir; it has been discovered by Amalitzky in Permian rocks of Russia[1347]. The Russian rocks in which _Glossopteris_ and _Gangamopteris_ were found are no doubt of Permian age. In Australia, South Africa, Brazil and Argentina, and in the Indian Coal-fields, _Gangamopteris_ is a characteristic genus of Lower Gondwana rocks. These strata are usually spoken of as Permo-Carboniferous in order to avoid the danger of attempting on insufficient data a precise correlation with European formations.

Feistmantel speaks of _Gangamopteris_ as most abundant in the Talchir-Karharbári beds, though it is represented also in the overlying Damuda series. In Australia the genus occurs in rocks which correspond in position and in their plant fossils with the Talchir-Karharbári beds of India; similarly, in South Africa and South America the Gangamopteris beds are homotaxial with those of India and Australia. The leaf described by Carruthers[1348] from Brazil as _Noeggerathia obovata_ (the type-specimen is in the British Museum) is no doubt specifically identical with _Gangamopteris cyclopteroides_ Feist.[1349] In a paper by Mr Hayden on Gangamopteris beds in the Vihi Valley, Kashmir, evidence is adduced in support of the conclusion that the rocks are “not younger than Upper Carboniferous and may belong to the base of that subdivision or even to the Middle Carboniferous[1350].” It would seem that _Gangamopteris_ was a very widely spread genus during the latter part of the Carboniferous period in the vast Southern Continent to which the name Gondwana Land is often applied, and that it flourished in the Southern Flora during at least part of the Permian period: with other members of the Glossopteris Flora it migrated to the North where it has been preserved in Permian rocks of Northern Russia. The Glossopteris Flora must have had its birth in the Southern hemisphere. The conclusion seems inevitable that the leaves of _Glossopteris_ and _Gangamopteris_ in the shales and sandstones of India, South Africa, South America, and Australia are relics of the vegetation of a continent of which these regions are the _disjuncta membra_. Darwin wrote to his friend Hooker in 1881, “I have sometimes speculated whether there did not exist somewhere during long ages an extremely isolated continent, perhaps near the South Pole[1351].” It is probable that _Gangamopteris_ is one of the genera which flourished on this continent.

_Gangamopteris cyclopteroides_, Feistmantel[1352]. Fig. 345.

1876. Feistmantel, Records Geol. Surv. India, Vol. IX. Pt iii. p. 73.

The specimen represented in fig. 345 illustrates the characters of this commonest representative of the genus.

[Illustration: FIG. 345. _Gangamopteris cyclopteroides_, Feist. (Nat. size. From Arber, after Feistmantel.)]

_Gangamopteris kashmirensis_, Seward.

1905. Seward, Mem. Geol. Surv. India, Vol. II. Mem. ii.

This type agrees closely with _G. cyclopteroides_ in size and in the form of the leaf, but it is distinguished by the flatter form of the arch formed by the lateral veins, by their greater inclination to the margin of the lamina, and by the more acutely pointed apex of the lamina. This species, though not very sharply distinguished from _G. cyclopteroides_, is important as coming from beds which have been assigned on other than palaeobotanical evidence to an Upper or possibly a Middle Carboniferous horizon[1353].

We have no definite information in regard to the nature of the reproductive organs of _Gangamopteris_, but such evidence as there is supports the view expressed by Dr White[1354] and shared by some other authors that _Gangamopteris_ and _Glossopteris_ should be assigned to the Pteridosperms. Despite the abundance of _Gangamopteris_ leaves, no fertile specimen has been discovered. This negative evidence may prove to be as correct as that which led Stur[1355] to exclude _Neuropteris_, _Alethopteris_ and _Odontopteris_ from the ferns. The only evidence of a positive kind is that furnished by Dr David White in his recent Report on the Palaeozoic Flora of South Brazil. This author describes some small Aphlebia-like leaves under two new generic names _Arberia_[1356] and _Derbyella_[1357]. The differences between the two sets of specimens, so far as can be determined from the reproductions of imperfect impressions, are slight, and it is by no means clear that a distinction of generic rank exists. These scale-leaves are on the average about 2 cm. in length; the lamina is oval or rounded and has more or less prominent lobes. In _Derbyella_ there are indications of anastomosing veins. The specimens referred to _Arberia minasica_ are, as White points out, very similar to the fossil described by Feistmantel from Lower Gondwana rocks of India as probably a portion of an inflorescence of _Noeggerathiopsis_[1358]. Feistmantel’s specimen is represented in fig. 346: the curled lobes may have originally borne seeds. In the Brazilian examples the abruptly truncated lobes “bear evidence of separation from reproductive bodies.” An important point is the association of these scale-leaves with _Gangamopteris_ fronds and with gymnospermous seeds of the _Samaropsis_ type. On the leaves assigned to _Derbyella aurita_ circular depressions occur at the base of the lobes which are described as probably due to sporangia.

Dr White’s discovery gives us increased confidence in expressing the view that _Gangamopteris_ bore its reproductive organs on specialised leaves very different from the sterile fronds; it also strengthens the suspicion that the genus is a member of the class of seed-bearing fern-like plants.

[Illustration: FIG. 346. _Arberia_ sp. (= _Noeggerathiopsis_ of Feistmantel). (Nat. size. After Feistmantel.)]

Lesleya.

This generic designation was instituted by Lesquereux[1359] for simple oval-linear leaves from the Coal-Measures of Pennsylvania. The leaves so named are probably generically identical with the specimen doubtfully assigned by Brongniart[1360] to the Coal-Measures, and made by him the type of the genus _Cannophyllites_ on the ground of a resemblance to the leaves of the recent flowering plant _Canna_. Fig. 347 illustrates the form of a _Lesleya_ leaf from the Coal-basin of Gard, named by Grand’Eury _L. simplicinervis_[1361], a type in which the veins are frequently unbranched and not repeatedly forked as in most examples of the genus (fig. 329, C). The features of the genus are, the oval-linear or lanceolate shape of the presumably simple frond, its entire or, in one species at least (_L. Delafondi_, Zeill.), finely dentate margin, the stout rachis giving off at a very acute angle numerous dichotomously branched secondary veins. In _L. Delafondi_ (fig. 329, C), described by Zeiller[1362] from the Lower Permian of Autun, the frond may reach a length of more than 20 cm. and a breadth of 8 cm. Similar species are represented by _L. ensis_[1363] from the coal-field of Commentry, and _L. grandis_[1364] from Upper Carboniferous rocks of North America. The genus is characteristic of Upper Carboniferous and Lower Permian strata: the form of the leaf and the direction of the secondary veins suggest comparison with _Glossopteris_, but in _Lesleya_ there are no cross-connexions between the veins. Nothing is known as to the fructification, a fact which naturally evokes the opinion that the genus is a Pteridosperm[1365] and not a true fern. Some years before the discovery of Pteridosperms, Grand’Eury[1366] suggested that _Lesleya_ might be a Gymnosperm; his opinion being based on the woody nature of the rachis and on the simple venation of _Lesleya simplicinervis_.

[Illustration: FIG. 347. _Leslya simplicinervis_, Grand’Eury. (Reduced: after Grand’Eury.)]

Neuropteridium.

In their monograph of fossil plants from the Bunter Series of the Vosges, Schimper and Mougeot[1367] described some pinnate leaves of ferns as species of the genus _Neuropteris_. In 1869 Schimper[1368] placed these in a new sub-genus _Neuropteridium_, in order to draw attention to the fact that their fronds appear to be simply pinnate and not bipinnate or tripinnate as in _Neuropteris_. The type-species of _Neuropteridium_ is _N. grandifolia_ Sch. and Moug. from the Bunter Sandstones of the Vosges. The genus includes Triassic European species and the widely distributed Permo-Carboniferous species from Brazil[1369] originally described by Carruthers as _Odontopteris Plantiana_. It is probable that some Carboniferous plants, particularly species from the lower members of the formation, referred to the genus _Cardiopteris_, are not genetically distinct from the Indian and southern hemisphere type _Neuropteridium validum_ (= _Odontopteris Plantiana_).

Fronds pinnate, linear; a broad rachis bears pinnules which may be either semicircular or broadly linear with an entire or lobed margin. The longer pinnules may exceed 6 cm. in length. The pinnules agree with those of _Neuropteris_ in being attached by the median portion of the lamina and not by the whole base, which is more or less auriculate. In some cases the repeatedly forked veins diverge from the centre of the pinnule base; in others there is a midrib which persists for a short distance only, and in some species the more persistent median vein gives the segments a closer resemblance to those of _Neuropteris_. Fructification unknown, with the exception of obscure indications of sporangia (?) on the fertile leaves of a Triassic species.

[Illustration: FIG. 348. _Neuropteridium validum_, Feist. Nat. size. From the Karharbári Coal-field, India. From Arber, after Feistmantel.]

_Neuropteridium validum._ (Feistmantel[1370]). Fig. 348.

1869. _Odontopteris Plantiana_, Carruthers, Geol. Mag. Vol. VI. p. 9, Pl. VI. figs. 2, 3.

1878. _Neuropteris valida_, Feistmantel, Mem. Geol. Surv. India, Foss. Flor. Gondwana Syst., Vol. III. p. 10, pl. II.–VI.

1880. _Neuropteridium validum_, Feistmantel, _Ibid._ 2, p. 84.

The specimen represented in fig. 348 illustrates the main features of _Neuropteridium validum_. This species is referred to by Dr White[1371] as _N. Plantianum_ on the ground of priority, and with a view to perpetuate the name of the English engineer Nathaniel Plant who discovered the species in a Brazilian Coal-field in the province of Rio Grande do Sul. Feistmantel’s specific name is however retained as being much better known. An examination of Mr Plant’s specimen in the British Museum led me[1372] to speak of the Brazilian species as identical with _N. validum_ described by Feistmantel from Lower Gondwana rocks of India. Zeiller[1373] had previously drawn attention to the resemblance between the two sets of specimens. The frond of _N. validum_ may exceed 50 cm. in length. The lower pinnules may be entire and semicircular in form while the upper and larger segments, which may reach a length of 5 or 6 cm., are characterised by broad lobes (fig. 348).

This type is represented in the flora of the Talchir-Karharbári series (Lower Gondwana) of India[1374], in Permo-Carboniferous rocks of Brazil and Argentine[1375], and in the sandstones of Vereeniging on the borders of the Transvaal and Cape Colony. It is a characteristic member of the Glossopteris Flora and occurs in association with _Glossopteris_ and _Gangamopteris_.

_Neuropteridium intermedium_ (Schimper). Fig. 349.

This species has been figured by Schimper and Mougeot[1376] from the Bunter of the Vosges and more fully described by Blanckenhorn[1377] from the Bunter beds of Commern. The pinnate leaves reach a length of 65 cm.; the lower semicircular pinnules pass gradually into broadly linear segments characterised by an auriculate base and a Neuropteris type of venation (fig. 354, D′, E). In the example reproduced in fig. 349 from one of Blanckenhorn’s figures, the fronds are attached to a short and thick rhizome bearing roots and portions of old petioles.

[Illustration: FIG. 349. _Neuropteridium intermedium_ (Schimp.). (After Blanckenhorn. ¼ nat. size.)]

An example of another Triassic species is afforded by _Neuropteridium grandifolium_ Schimp. and Moug., which agrees very closely with _N. validum_ in the size and shape of the pinnules. The occurrence in Lower Mesozoic European rocks of fronds hardly distinguishable from the older southern species may be regarded as favourable to the view already expressed, that some at least of the Permo-Carboniferous plants migrated north of the Equator. The resemblance between the Vosges Triassic species of _Schizoneura_[1378] and the examples of this genus recorded from the Lower Gondwana rocks of India affords additional evidence of a northern migration.

Our knowledge of the reproductive organs of _Neuropteridium_ is practically _nil_. There is no doubt that Zeiller[1379] and Blanckenhorn[1380] are correct in regarding the Bunter fronds assigned by Schimper and Mougeot to the genus _Crematopteris_ as the fertile leaves of _Neuropteridium intermedium_ or some other species from the same horizon. These fronds bear crowded pinnules similar to those of _Neuropteridium intermedium_, _N. Voltzii_[1381], and other species, exhibiting on the exposed surface numerous carbonaceous spots which may be the remains of sporangia.

Cardiopteris.

Schimper[1382] applied this generic name to Lower Carboniferous fronds of a simple-pinnate habit which had previously been described as species of _Cyclopteris_. _Cardiopteris frondosa_ may serve as a typical example. This species, originally described by Goeppert as _Cyclopteris frondosa_ (fig. 350), is recorded from Lower Carboniferous rocks in the Vosges district[1383] in Silesia, Moravia[1384], and Thuringia[1385]. The pinnules, which are attached in opposite pairs to a broad rachis, vary in length from 2 to 10 cm. and have a breadth of 2 to 8 cm.; in manner of attachment and venation they agree with those of _Neuropteridium validum_. The venation is very clearly shown in a drawing of some large pinnules figured by Stur[1386].

The specimen of _Cardiopteris frondosa_, a portion of which is shown in fig. 350 on a slightly reduced scale, was originally figured by Schimper from an unusually good example in the Strassburg Museum. Schimper’s drawing hardly does justice to the original specimen.

A frond bearing rather narrower pinnules, alternately placed on the rachis, which Fritsch has described as _Cardiopteris Hochstetterii_ var. _franconica_ from the Culm of Thuringia, bears a close resemblance to _Neuropteridium validum_ but differs in the entire margin of the pinnules. An Upper Carboniferous species from Russia described by Grigoriew[1387] as _Neuropteris_, cf. _cordata_ var. _densineura_, represents another form of similar habit.

[Illustration: FIG. 350. _Cardiopteris frondosa_ (Goepp.). (¾ nat. size. After Schimper.)]

Schuster[1388] has recently proposed a new generic name _Ulvopteris_ for a fragment of a pinna from the Coal-Measures of Dudweiler in Germany bearing large pinnules, which he compares with those of _Cardiopteris_ and species of _Rhacopteris_. The specimen appears to be indistinguishable from some of those already referred to as conforming to _Neuropteridium_, and it is difficult to recognise any reason for the creation of a new generic name.

We cannot hope to arrive at any satisfactory decision in regard to the precise affinity between _Neuropteridium validum_ and species referred to _Cardiopteris_ and other genera so long as portions of sterile fronds are the only tests at our disposal. It is difficult to determine whether a specimen consisting of an axis bearing pinnules represents a large pinna of a bipinnate frond or if it is a complete pinnate leaf. There is, however, no adequate reason for supposing that the presumably pinnate fronds from the Gondwana Land rocks are generically distinct from the Lower Carboniferous European species _Cardiopteris frondosa_. Granting the probability that both genera are Pteridosperms and closely allied to one another, the two generic names may be retained on the ground of long usage and in default of satisfactory evidence confirmatory of generic identity. _Cardiopteris_ would thus stand for a type of frond characteristic of the Lower Carboniferous strata of Europe, while _Neuropteridium_ is retained for the Southern species _N. validum_, and for others from the Trias of the Vosges.

Aphlebia.

This name was proposed by Presl[1389] for large leaf-like impressions having a pinnate or pinnatifid form and characterised by a confused irregular type of venation, or by a fine superficial striation or wrinkling which simulates veins. Gutbier had previously described similar fossils as _Fucoides_, and other authors have described Aphlebiae as species of _Rhacophyllum_, _Schizopteris_, and other genera[1390]. The term _Aphlebia_ is retained, not as denoting a distinct genus but (i) as a descriptive name for detached leafy structures similar to those figured by Presl, which are now recognised as laminar appendages of the petioles of ferns or fern-like fronds, and (ii) as an epithet for highly modified pinnules which frequently occur at the base of the primary pinnae of Pecopteroid and Sphenopteroid fronds (e.g. _Dactylotheca plumosa_, fig. 293)[1391].

Modified pinnules, similar in their reduced and deeply dissected lamina to those represented in fig. 293, are frequently found at the base of the primary pinnae of Palaeozoic species of _Sphenopteris_ and other genera of Pteridosperms or ferns, including members of the Coenopterideae. Potonié[1392] gives a list of various types of Aphlebiae in his paper on these organs. A striking case has recently been described by Zeiller in a French Upper Carboniferous species, _Sphenopteris Matheti_[1393]. It would seem that the larger examples of Aphlebiae are more frequently associated with the compound leaves of Pteridosperms than with those of Ferns[1394].

As examples of the larger types of Aphlebiae reference may be made to _Aphlebia crispa_ (Gutb.)[1395], which reaches a length of nearly 60 cm. and has the form of a more or less triangular pinnate leaf divided into decurrent deeply lobed segments, to a similar species represented by _A. Germari_ (= _Schizopteris lactuca_ Germ.)[1396] which simulates the leaves of endive (_Cichorium endivia_ L.), and to some large forms figured by Grand’Eury[1397] as species of _Schizopteris_.

Aphlebiae such as that figured by Kidston[1398] as _Rhacophyllum crispum_, with narrow ultimate segments, might easily be mistaken for the impressions of an alga.

The term _Aphlebia_ may be applied also to the Cyclopteroid pinnules on the petioles of some species of _Neuropteris_, _Odontopteris_ and _Archaeopteris_. Goebel[1399] has referred to the application by Potonié and other authors of the term Aphlebioid to the pinnules which serve as bud-protecting organs in recent fronds of _Gleichenia_ (fig. 226, p. 290); he expresses the opinion that it is superfluous and misleading to make use of a special designation for structures which are undoubtedly modified pinnules. In the case of fossils it is, however, convenient to employ the term _Aphlebia_ as a descriptive name for modified pinnules or stipular structures which cannot be connected with definite species of fronds. It is clear that some Aphlebiod leaflets, such as those of _Dactylotheca_, served as protective organs for the unexpanded pinnae[1400], and in all probability the large Aphlebiae served the same purpose as the fleshy stipules of _Angiopteris_ and _Marattia_ which cover the uncoiled fronds. The pinnatifid scale-leaves of considerable size (fig. 351) which occur in the leaf-axils or as ochrea-like stipules on the fronds of _Gunnera_ (a tropical and subtropical Dicotyledonous genus) bear a very close resemblance to some Palaeozoic Aphlebiae, e.g. _Aphlebia crispa_ (Gutb.). The recent and fossil scale-leaves may be regarded as similar in function as in form; moreover the delicate coiled fronds of Palaeozoic Pteridosperms or ferns, like those of some recent flowering plants, may have been kept moist by a secretion of mucilage. The pinnatifid stipules of _Marattia fraxinea_ (fig. 241, B, p. 317) resemble certain fossil Aphlebiae, and the wrinkled surface of the recent stipules presents an appearance similar to that which in some fossil forms has been erroneously described as veining. It is not improbable that mantle-leaves of such recent ferns as _Polypodium quercifolium_ (fig. 234, M, p. 303) are comparable with some fossil Aphlebiae which may have served as humus-collectors for Palaeozoic epiphytes.

[Illustration: FIG. 351. Scale-leaf of _Gunnera manicata_. (Slightly reduced. M.S.)]

The filiform appendages on the petioles of the recent fern _Hemitelia capensis_ (fig. 235, p. 304) have often been compared with the aphlebioid leaflets of fossil fronds.

Potonié who has discussed the nature of Aphlebiae regards them as vestiges of a once continuous lamina, which formed a winged border to the branched axes of more primitive forms of fronds. It is possible that the pinnules between the pinnae on the rachis of _Archaeopteris_ and the Cyclopteroid leaflets of _Neuropteris_ and _Odontopteris_ may have the morphological significance attributed to them by Potonié. In some cases it is probable that the Aphlebiae, whether vestiges or not, served the purpose of protecting either the whole frond or individual pinnae. Aphlebiae, though especially characteristic of Palaeozoic leaves, are occasionally met with in the form of modified pinnules at the base of the primary pinnae on Mesozoic ferns, e.g. in _Coniopteris hymenophylloides_[1401].

In some fern fronds the lowest pinnule of each pinna differs in shape or size from the normal ultimate segments, but it would be almost affectation to extend the use of the term _Aphlebia_ to such pinnules. The Jurassic species _Cladophlebis lobifolia_ (Phill.) is a case in point[1402]. In this fern, which some authors speak of, without sufficient reason, as _Dicksonia lobifolia_[1403], the lowest pinnule is large and different in shape from the others.

[Illustration: FIG. 352.

A. _Sphenopteris obtusiloba_. Pinnule. (Enlarged. After Zeiller.) B, C. _S. obtusiloba_. (⅞ nat. size. After Zeiller.) D. _Pecopteris arborescens_. (Slightly enlarged. After Zeiller.) E. _Sphenopteris furcata_ (= _Diplotmema furcatum_). (Slightly enlarged. After Zeiller.)]

Sphenopteris.

_Sphenopteris_ is one of the many generic names which we owe to Brongniart[1404]. It is the generic designation used for a great number of Palaeozoic and later fronds, most of which are those of true ferns while some Palaeozoic species are undoubted Pteridosperms. The genus, which is purely provisional, includes members of widely different families possessing pinnules of the same general type, such as is represented in some recent species of _Davallia_, _Asplenium_, and other ferns.

The fronds of _Sphenopteris_ may be bipinnate, tripinnate, or quadripinnate; the rachis may be dichotomously branched or the branching may be of the pinnate type characteristic of most recent ferns. The pinnules are small; they vary considerably in shape even in a single frond, but the chief characteristics are: the lobed lamina, contracted and often wedge-shaped at the base (fig. 352), the dichotomously branched veins radiating from the base or given off from a median rib at an acute angle. The lamina may be divided into a few bluntly rounded lobes (fig. 352, C) or deeply dissected into linear or cuneate segments (fig. 352, A, B, E).

Examples of Sphenopteroid leaves have already been described under the genera _Coniopteris_, _Onychiopsis_, _Ruffordia_, etc. Among the numerous examples of _Sphenopteris_ species from the Carboniferous rocks mention may be made of _Sphenopteris obtusiloba_ Brogn.[1405] (fig. 352, A–C), which occurs in the Middle and Lower Coal-Measures of Britain[1406]. This type is characterised by the almost orbicular, oval or triangular pinnules which may reach a length of 15 mm.; they are occasionally entire, but more usually divided into 3 to 5 rounded lobes. The forked veins radiate from the base of the pinnule. The rachis may be dichotomously branched. Fructification unknown.

The species _S. furcata_ Brongn.[1407], characteristic of the Middle and Lower Coal-Measures of Britain (fig. 352, E), is referred to under Stur’s genus _Diplotmema_[1408] in which it is included by some authors solely because of the dichotomous habit of branching of the pinnae.

The pinna represented in fig. 353 illustrates a similar type of pinnule. This species, which is very common in the Calciferous Sandstone of Scotland, was described by Lindley and Hutton as _Sphenopteris affinis_[1409].

The fronds of _Sphenopteris affinis_ were discovered by Mr Peach[1410] in a fertile condition, but he regarded the reproductive organs as those of a plant parasitic on the _Sphenopteris_ fronds. Kidston[1411] substituted Stur’s genus _Calymmatotheca_ for _Sphenopteris_ on the ground that the sporangia figured by Peach under the name _Staphylopteris Peachii_ bear a close resemblance to the organs which Stur described as valves of an indusium in his species _Calymmatotheca Stangeri_[1412]. An examination of Stur’s specimens by Miss Benson[1413] and by Prof. Oliver and Dr Scott has confirmed Stur’s interpretation of the appendages at the tips of the fertile pinnae as valves of an indusial or cupular structure. The superficially similar bodies on the fertile pinnae of _S. affinis_ are however true sporangia, and cannot legitimately be included in the genus _Calymmatotheca_ as described by Stur. For this reason Miss Benson institutes a new genus _Telangium_, the type-species of which, _T. Scotti_ from the Lower Coal-Measures of Lancashire, is based on petrified material. The Scotch species _Sphenopteris affinis_ (= _Calymmatotheca affinis_ of Kidston) is also transferred to _Telangium_; the sporangia are considered by Miss Benson to be microsporangia. This with other species is no doubt correctly included in the Pteridosperms. A complete frond of _Sphenopteris affinis_, showing a regular dichotomy of the main axes, is represented by an admirable drawing in Hugh Miller’s _Testimony of the Rocks_[1414].

[Illustration: FIG. 353. _Sphenopteris affinis_, Lind. and Hutt. From the Calciferous Sandstone of Burdiehouse (Scotland). (Sedgwick Museum, Cambridge.) M.S.]

Some of the Palaeozoic species of _Sphenopteris_ probably represent the fronds of true ferns, but others are known to have been borne by Pteridosperms. _S. Hoeninghausi_ (fig. 290, C, p. 399) is the foliage of _Lyginodendron_, and Scott[1415] speaks of three species, _S. dissecta_, _S. elegans_, and _S. Linkii_ as the leaves of _Heterangium_. Grand’Eury[1416] has recorded the occurrence in French Coal-Measures of seeds in association with other Sphenopteroid fronds.

Mariopteris, Diplotmema, Palmatopteris.

The discovery of sporangia on the fronds of several Palaeozoic species of _Sphenopteris_ and _Pecopteris_ has led to the institution of new generic names, which indicate an advance in knowledge beyond the stage implied by the use of those provisional designations based solely on the form and venation of the pinnules. Other names have been created by authors in place of _Sphenopteris_ and _Pecopteris_ on the ground that a striking feature in the mode of branching of fronds is sufficiently important to justify generic recognition even in the absence of fertile specimens. As examples of designations based primarily on the branch-system of compound leaves, the genera _Mariopteris_, _Diplotmema_, and _Palmatopteris_ may be briefly considered (fig. 354 A–C). Dr Kidston[1417] is of opinion that the creation of new genera for purely vegetative characters of fronds is of no real advantage, and he prefers to retain the older provisional names for species known only in the sterile condition. On the other hand, if we are sufficiently familiar with specimens large enough to enable us to recognise a well-defined morphological character, it may serve a useful purpose to employ a generic designation for features which may have a phylogenetic value. A comparative examination of Palaeozoic, Mesozoic, and recent compound fronds, including both Pteridosperms and true ferns, brings to light certain distinguishing features characteristic of the older types which, as Potonié maintains[1418], point to the derivation of the pinnate habit from a primitive dichotomous system of branching. For a more complete discussion of this question reference should be made to Potonié’s suggestive papers. Among recent ferns _Matonia_ and _Dipteris_, two survivals from the past, afford instances of fronds with a branching system of the dichotomous type.

Similarly, in _Gleichenia_, _Lygodium_, and more rarely in species of Polypodiaceae (_e.g._ _Davallia aculeata_, fig. 232) dichotomy is a striking feature of the fronds. In the great majority of recent ferns the fronds have assumed a pinnate habit. Among Palaeozoic fern-like fronds dichotomous branching of the main rachis and of the pinnae is much more common. Potonié draws attention to several other features which distinguish Palaeozoic fronds from the majority of later species: the frequent occurrence of pinnules borne directly on the main rachis (fig. 354, D), and of modified pinnules or Aphlebiae on the rachis and petiole, are characters to which he attributes an evolutionary significance. The main point is that a comparative examination of leaf-form affords evidence in favour of the view that the modern type of frond, with its naked rachis bearing two rows of pinnae, has been derived from a less specialised type in which the distinction between the parts of the leaf is much less evident. The primitive leaf was probably a dichotomously branched axis provided with a continuous lamina which eventually became broken up into separate lobes or pinnules.

As the dichotomy of the frond became less regular, a pinnate habit was acquired, as is clearly seen in many Palaeozoic types which constitute connecting links between forked and pinnate fronds (fig. 354, D). The Aphlebiae may be remnants of the once-continuous lamina on the petiole, and the normal pinnules borne on the rachis may be regarded as the attributes of fronds in which the division of physiological labour had not reached the stage which characterises the leaves of recent ferns.

_Mariopteris._

This name, which is due to Zeiller[1419], is applied by him to Palaeozoic fronds characterised by a double bifurcation of the rachis of the primary pinnae. _Mariopteris muricata_ (= _Pecopteris muricata_ Schloth.) may be taken as the type of the genus. This species is common in the Lower and Middle Coal-Measures of Britain and rare in the Upper Coal-Measures[1420]. It is described by Kidston[1421] as one of the most polymorphic and widely distributed Coal-Measure species. The pinnules as seen in fig. 364, B, are of the Sphenopteroid type. No fertile specimens are known, but it is significant that Grand’Eury[1422] has recorded the association of _Mariopteris muricata_ and seeds.

The main rachis gives off alternate naked branches, each of which bifurcates at its apex into two short naked axes, and these are again forked, the ultimate branches having the form of bipinnate pinnae provided with large Sphenopteroid pinnules (fig. 354, B). Zeiller includes in _Mariopteris_ some species which Stur[1423] referred to his genus _Diplotmema_. Possibly some of the Palaeozoic fronds with a zigzag rachis may have been climbers like _Lygodium_.

[Illustration: FIG. 354.

A. _Palmatopteris._ B. _Mariopteris._ (A, B, after Potonié.) C. _Diplotmema Zeilleri_, Stur. (After Zeiller.) C′. _D. Zeilleri._ Pinnule. (× 3. After Zeiller.) D. _Neuropteris macrophylla._ (British Museum.) D′. _N. macrophylla._ Pinnule. (Slightly enlarged. After Kidston.) E. _N. heterophylla._ Pinnule. (Slightly enlarged. After Zeiller.) F. _N. Scheuchzeri._ (Slightly reduced. After Kidston.) G. _Alloiopteris Essinghii._ (Enlarged. After Potonié.)]

_Diplotmema._

This generic name is employed by Zeiller[1424] and other authors in a more restricted sense than that in which it was originally used by Stur. The Upper Carboniferous species _Sphenopteris furcata_ Brongn. (fig. 352, E) may serve as the type. This species occurs in the Middle and Lower Coal-Measures of Britain[1425]. The main rachis gives off branches as in _Mariopteris_, but in _Diplotmema_ each naked lateral branch is forked at its apex into two opposite pinnae bearing deeply dissected Sphenopteroid pinnules. Zeiller[1426] and Stur have recorded fertile specimens of _Diplotmema_, but in no case have actual sporangia been discovered. In the species _Diplotmema Zeilleri_ Stur (fig. 354, C, C′) two Aphlebiae occur at the base of each secondary axis[1427]. It has been pointed out by Potonié that in _Diplotmema furcatum_ the equal dichotomy of the lateral branches is not characteristic of the frond as a whole. In the case of branches higher on the rachis the dichotomy becomes unequal and the forked axis is gradually replaced by a simple pinna (fig. 354, A). For this type of frond, Potonié proposed the generic name _Palmatopteris_ in place of _Diplotmema_, which he discards. The long comparatively slender rachis of _P. furcata_ suggests comparison with the liane species of _Lygodium_[1428].

[Illustration: FIG. 355.

A. _Cephalotheca mirabilis_, Nath. Fertile pinnae. (Partially restored. After Nathorst.) B. _C. mirabilis._ Sterile pinnule. Nat. size. (After Nathorst.)]

Cephalotheca.

This genus was proposed by Nathorst[1429] for some peculiar bipinnate fertile fronds from the Upper Devonian rocks of Bear Island. The pinnae bear slender forked ultimate segments represented by a few detached fragments (fig. 355, B), associated with the rachises. The fertile pinnae are given off in opposite pairs from the main axis over which they are concrescent (fig. 355, A). A mop-like cluster of sporangia is borne on the lower surface and close to the base of a fertile pinna: the exannulate sporangia are compared with those of _Scolecopteris_. Nathorst compares _Cephalotheca_ with a Belgian species of Upper Devonian age described by Crépin[1430] as _Rhacophyton condrusorum_ and by Gilkinet[1431] as _Sphenopteris condrusorum_. A similar fossil is also described by Baily[1432] as _Filicites lineatus_ from the Kitorkan Grits of Ireland.

The position of _Cephalotheca_ cannot be definitely determined from the available data, but it is more probable that it was a seed-bearing Pteridosperm and not a true fern. Zeiller[1433] has recently expressed the same opinion.

Thinnfeldia.

The genus _Thinnfeldia_, founded by Ettingshausen in 1852[1434] on some Hungarian Liassic specimens, though frequently included in the Filicales, cannot be said to occupy that position by virtue of any well-authenticated filicinean features. It is by no means improbable that many of the species referred to this genus are closely allied to Palaeozoic Pteridosperms.

_Thinnfeldia_ may be briefly defined as follows:

Fronds simple and pinnatifid, pinnate or bipinnate: rachis broad and occasionally dichotomously branched. Pinnules often fleshy or coriaceous; broadly linear, entire or lobed, provided with a midrib from which simple or forked secondary veins are given off at an acute angle: or the laminae may be short and broad without a midrib and traversed by several slightly divergent and forked veins.

No satisfactory evidence of reproductive organs has so far been adduced.

The genus is chiefly characteristic of Upper Triassic, Rhaetic, and Jurassic floras, though it was in all probability represented in Permian floras. Several species, many of which are valueless, are recorded also from Cretaceous and Tertiary formations. Search should be made for fertile specimens or for evidence as to the association of seeds with _Thinnfeldia_ fronds.

Some Permian fossils from Kansas which Sellards[1435] has made the type of a new genus, _Glenopteris_, appear to be indistinguishable generically from leaves of Lower Mesozoic age universally recognised as typical examples of _Thinnfeldia_.

_Thinnfeldia odontopteroides_ (Morris)[1436]. Figs. 356–358.

This is a very variable species as regards the shape and size of the ultimate segments and their venation. It is a type of extended geographical range characteristic of Rhaetic or Upper Triassic rocks in Australia, South Africa, India, South America, and various European localities.

Frond bipinnate; the broad rachis may be dichotomously branched. Pinnules with a thick lamina which may be almost semicircular in form, deltoid, broadly oval or broadly linear, and often confluent at the base. Short and broad pinnules occur on some fronds directly attached to the main rachis between the pinnae. The longer and narrower pinnules (fig. 356, C), resembling those of the Palaeozoic genus _Alethopteris_, have a well-defined midrib, while the smaller segments are characterised by several slightly divergent veins which spring directly from the rachis (fig. 356, A). Epidermal cells polygonal or, above the veins, rectangular in shape; stomata, which are slightly sunk, occur on both the upper and lower epidermis. Fertile specimens unknown.

The portion of a lobed pinnule shown in fig. 356, B, illustrates a form of segment intermediate between the linear type with a midrib and a row of shorter pinnules without a median vein. Fig. 356, D, represents another instance of variation in the arrangement of the veins in segments of different sizes. Various specific and generic names have been assigned to Thinnfeldia fronds of Rhaetic age on the ground of the occurrence of pinnules longer and narrower than those usually associated with _T. odontopteroides_; but in view of the range of variation met with in a single leaf it is advisable to extend rather than to restrict the boundary of what we are pleased to regard as a specific type.

[Illustration: FIG. 356.

A–D. _Thinnfeldia odontopteroides_ (Morris). E. _Ptilozamites._ (E, after Nathorst.)]

The name _Thinnfeldia lancifolia_ has been applied by Morris to fossils from Australia which may be identified with _T. odontopteroides_, and the same designation is employed by Szajnocha and by Solms-Laubach[1437] for Rhaetic specimens from South America. Similar fronds are described by Geinitz[1438] as _Thinnfeldia tenuinervis_ from Argentine Rhaetic strata. _Odontopteris macrophylla_ Curran, _T. falcata_ Ten.-Woods, _Gleichenia lineata_ Ten.-Woods, and _Cardiopteris Zuberi_ Szaj. afford other examples of what are probably closely allied forms[1439].

[Illustration: FIG. 357. _Thinnfeldia odontopteroides_ (Morris). ⅘ nat. size.]

Some exceptionally large examples of _T. odontopteroides_ are figured by Feistmantel[1440] from the Hawkesbury series of New South Wales in which the bipinnate frond has a breadth of 25–30 cm. A specimen from the Molteno beds of South Africa, probably of Rhaetic age, represented in fig. 357, illustrates a smaller leaf with pinnules of the linear type, some of which are partially divided into shorter pinnules with forked veins. The example represented in fig. 358, from Cyphergat (S. Africa), shows two equal branches of a rachis with small contiguous segments.

[Illustration: FIG. 358. _Thinnfeldia odontopteroides_. From a specimen in the British Museum (v. 2490). 1½ nat. size.]

Some specimens figured by Zeiller[1441] from the Rhaetic strata of Tonkin as _Pecopteris (Bernouillia?_) sp. may be portions of _Thinnfeldia_ fronds, and the large leaves which he refers to _Ctenopteris Sarreni_ differ but slightly from the Australian specimens described by Feistmantel as _T. odontopteroides_.

_Thinnfeldia rhomboidalis_, Ettingshausen. Figs. 359, 360, C.

Under this name Ettingshausen described the type-specimen of the genus from Lower Lias strata at Steierdorf in Hungary. He assigned the plant to the Coniferae on the ground of a resemblance of the pinnules to the phylloclades of _Phyllocladus. Thinnfeldia rhomboidalis_ bears a close resemblance to _T. odontopteroides_, but the pinnules are usually longer and narrower, as shown in the English specimen from the Lower Lias of Dorsetshire represented in fig. 359. The darker margin of the pinnules shown in fig. 360, C, gives the impression of a revolute lamina, but a microscopical examination points to a thicker cuticle at the edge of the segments.

[Illustration: FIG. 359. _Thinnfeldia rhomboidalis_, Ettings. Slightly reduced. From an English Liassic specimen in the British Museum. [M.S.]]

The species is recorded from Jurassic rocks of France, Germany, Italy, India, Australia, and elsewhere[1442].

Palaeobotanical literature contains numerous records of Jurassic, Cretaceous and some Tertiary species referred to _Thinnfeldia_, but many of these are probably not generically identical with _T. odontopteroides_ or _T. rhomboidalis_. Mr Berry[1443] in a paper on _The American species referred to Thinnfeldia_ concludes that the genus is “a rather indefinite one ... and badly in need of revision.” He regards the Middle and Upper Cretaceous American species as Conifers related to _Phyllocladus_ and probably forming a link between the Podocarpeae and Taxeae: for these forms he proposes the generic name _Protophyllocladus_. The opinion has been expressed elsewhere[1444] that this “problematical[1445]” genus rests on an unsatisfactory basis; the available data do not justify the use of a name which implies the existence in North American Cretaceous floras of a type related to the New Zealand and Tasmanian Conifer _Phyllocladus_. We are not in a position to assign a single species of _Thinnfeldia_ to the Filicales or the Gymnosperms.

A leaflet from Jurassic rocks of Poland figured by Raciborski[1446] shows what this author regards as the impression of a circular sorus: no sporangia have been found. A specimen in the British Museum[1447], which is said to come from Rhaetic beds in Queensland, shows a row of contiguous polygonal prominences on each side of the midrib which resemble the sori of a fern; but until sporangia are discovered we cannot determine the precise nature of this apparently fertile frond.

A species described by Fontaine[1448] from the Potomac beds (Wealden-Jurassic) of North America as _Thinnfeldia variabilis_ affords a good example of a plant which cannot be identified with any degree of confidence either as a fern or a seed-bearing type. Mr Berry draws attention to the former application of this name by Velenovský to a distinct Lower Cretaceous Bohemian species and proposes for Fontaine’s plant the name _T. Fontainei_; he maintains that no one has doubted the fern-nature of the Potomac plant. _T. variabilis_ may indeed be a fern, but the evidence is not such as to preclude legitimate doubts as to the correctness of this suggestion. Solms-Laubach[1449], in referring to Schenk’s view that _Thinnfeldia_ and its allies may represent a group intermediate between Ferns and Gymnosperms, admits that it is a possible supposition; he is, however, inclined to consider _Lomatopteris_ and _Cycadopteris_, “genera especially comparable with _Thinnfeldia_” as more probably ferns.

At this point we may conveniently consider a series of genera which occupy an equally uncertain position and bear a very close resemblance to _Thinnfeldia_.

[Illustration: FIG. 360.

A. _Lomatopteris jurensis_. (⅞ nat. size. After Kurr.) B. _L. Schimperi_. (⅞ nat. size. After Salfeld.) C. _Thinnfeldia rhomboidalis_, Ett. (Slightly enlarged. British Museum. No. 52672.)]

Lomatopteris.

The generic name _Lomatopteris_ was proposed by Schimper[1450] for some bipinnate fronds originally described by Kurr[1451] from Jurassic rocks of Württemberg as _Odontopteris (?) jurensis_ (fig. 360, A). I have elsewhere expressed the opinion[1452] that this German species may be identical with _Thinnfeldia rhomboidalis_ Ett. Kurr’s type-specimen, a portion of which is reproduced in fig. 360, A, consists of a frond or large pinna characterised by a prominent and broad rachis giving off alternate linear pinnae bearing bluntly rounded, contiguous and basally concrescent pinnules having a thick or revolute border and a central rib. The lateral veins are visible in the ultimate segments of Kurr’s fossil. Saporta[1453] has described several species, which he refers to Schimper’s genus, from French Jurassic strata: it is, however, difficult to recognise some of the examples represented in his illustrations as specifically distinct forms. This author notices the resemblance of _Lomatopteris_ to _Thinnfeldia_, not only in habit but in the structure of the epidermal cells[1454]. In _Lomatopteris_ and in _Thinnfeldia_ the cells have straight and not sinuous walls and the slightly sunken stomata are surrounded by a ring of epidermal cells. Salfeld[1455] has recently described portions of fronds from Jurassic rocks of South-West Germany, which he identifies as _Lomatopteris jurensis_. He disagrees with my view that _Lomatopteris_ does not differ sufficiently from _Thinnfeldia_ to be accorded generic autonomy, chiefly on the ground that the folded-over edge of the pinnules is a distinguishing feature of _Lomatopteris_. There is, however, no difference, in appearance at least, between the leaflets of some species of _Thinnfeldia_, e.g. _T. rhomboidalis_ from Liassic rocks of England[1456], and those referred to _Lomatopteris_. In a later paper, Salfeld[1457] describes some Portlandian fragments from North Germany as _Lomatopteris Schimperi_, identifying them with a Wealden fossil of somewhat doubtful affinity, which Schenk[1458] makes the type of his species. The Portlandian specimens are described as tripinnate, with thick decurrent obtusely terminated pinnules with a revolute edge. The general form of the frond is very similar to that of _L. jurensis_. Salfeld publishes a photograph of a large specimen which he describes as fertile and a drawing of a piece of a pinna: the latter is reproduced in fig. 360, B. He speaks of sori occurring in two rows, probably attached to lateral veins, in the groove between the midrib and the revolute edge of the lamina. The sporangia are described as “nicht näher bekannt[1459].” An examination of the figures reveals nothing as to the nature of the “sori.” The specimens are considered by Salfeld to afford decisive evidence against the view that _Lomatopteris_ and _Thinnfeldia_ are generically identical. Nothing has so far been published which constitutes a valid argument in favour of retaining Schimper’s generic name.

Cycadopteris.

Zigno[1460] founded the genus _Cycadopteris_ on Italian Jurassic impressions regarded by Schimper as indistinguishable from _Lomatopteris_. As Solms-Laubach[1461] points out, the supposed sori of _Cycadopteris_ described by Zigno are not convincing. There appear to be no satisfactory reasons for separating _Cycadopteris_ from _Lomatopteris_, nor do the fronds described under these names exhibit any important differences from _Thinnfeldia_.

Ptilozamites.

Nathorst[1462] founded this genus on a remarkable series of specimens from the Rhaetic Coal-beds of Scania and assigned it to the Cycadophyta. The species _Ptilozamites Heeri_ may be taken as a representative type. The leaves are linear and simply pinnate. In the example shown on a much reduced scale in fig. 361 the frond is 53 cm. long and 2·1 cm. broad. The upper edge of each pinnule is straight or slightly concave; the lower edge is rounded; the veins are slightly divergent and dichotomously branched (fig. 356, E, p. 539). In some of Nathorst’s specimens the broad rachis is forked as in many Thinnfeldias.

As a comparison of fig. 356, A and E, shows, the pinnules of some specimens of _Thinnfeldia odontopteroides_ are identical with those of _Ptilozamites_. In the latter genus the rachis is either unbranched or occasionally forked, while in _Thinnfeldia_ the branching may be of the dichotomous or pinnate type. In _Ptilozamites_ the segments appear to be always without a midrib, while a median vein frequently occurs in those of _Thinnfeldia_. There can be little doubt as to the very close alliance between the Rhaetic species referred to these two genera. The name _Ptilozamites_ should perhaps be retained for such long and narrow fronds as that shown in fig. 361: no species included in _Thinnfeldia_ is known in which the rachis reached so great a length without branching. The habit of _Ptilozamites Heeri_ predisposes one in favour of Nathorst’s opinion that the fronds are Cycadean: we have no information in regard to the nature of the reproductive organs.

[Illustration: FIG. 361. _Ptilozamites Heeri_, Nath. (⅓ nat. size. After Nathorst.)]

Ctenopteris.

This name was instituted by Saporta[1463], at Brongniart’s suggestion, for Liassic species characterised by pinnules like those of _Thinnfeldia_, but distinguished by the bipinnate habit of the frond. Saporta compares the genus with the Palaeozoic leaves known as _Odontopteris_, and with Italian Jurassic plants referred by Zigno to his genus _Dichopteris_.

The name _Ctenozamites_ is applied by Nathorst[1464] to the type of frond which Saporta, Zeiller, and other authors refer to _Ctenopteris_. Nathorst instituted _Ctenozamites_ for fossils agreeing in the form and venation of the pinnules with his genus _Ptilizamites_ but differing in being bipinnate and not pinnate.

Fronds of _Ctenopteris_ are characteristic of the Jurassic and Rhaetic series; they are known only in the sterile condition. As Zeiller[1465] says, _Ctenopteris_ may be a member of the Cycadofilices, an extinct group founded on Palaeozoic plants combining Cycadean and Filicinean characters, and some of which are now known to be Pteridosperms. It is probable that the genus is not a true fern: it is more likely to be a member of the Cycadophyta or of some generalised extinct group.

_Ctenopteris cycadea_ (Brongniart). Fig. 362.

1828. _Filicites cycadea_, Brongniart, Hist. Vég. foss. p. 387, Pl. CXXIX.

1832. _Odontopteris cycadea_, Berger, Verstein. Coburg Geg. p. 23, Pl. III.

1873. _Ctenopteris cycadea_, Saporta, Pal. Franç. Vol. I. p. 355, Pls. XL. XLI.

Frond bipinnate, broad rachis giving off branches at an acute angle; pinnules broadly linear, slightly falcate, with several slightly divergent forked veins.

A frond very similar to the Lower Lias specimen from Dorsetshire represented in fig. 362 was described by Leckenby as _Ctenis Leckenbyi_ (Bean MS.) from the Inferior Oolite of Yorkshire[1466]. Leckenby recognised the possibility of a Cycadean affinity, but regarded the bipinnate habit as an objection. The branched fronds of the Australian Cycad _Bowenia_ supply an answer to this objection. Several good examples of _Ctenopteris cycadea_ are figured by Schenk[1467] from Rhaetic rocks of Persia. Zeiller’s Tonkin Rhaetic species, _C. Sarrani_[1468], affords a striking illustration of the difficulty of drawing a clear line of separation between _Ctenopteris_ and some species of _Thinnfeldia_.

[Illustration: FIG. 362. _Ctenopteris cycadea_, Brongn. (½ nat. size.) From a specimen in the British Museum. [M.S.]]

_Ctenopteris_ is in all probability very closely related to _Thinnfeldia_ and _Ptilozamites_.

Dichopteris.

This genus was proposed by Zigno[1469] for some large specimens from the Jurassic plant-beds of Northern Italy.

The bipinnate leaves are characterised by the great breadth of the rachis which is dichotomously branched in the distal region (fig. 363); the linear pinnae reach a considerable length. Pinnules relatively small, oblong and slightly contracted at the base; the decurrent and confluent lamina forms a narrow wing to the main axis. Veins slightly divergent and forked, as in _Ptilozamites_.

_Dichopteris visianica_, Zigno. Fig. 363.

A specimen of this species in the Padua Museum has a total length of 83 cm. It has been elsewhere suggested[1470] that a fragment figured by Zigno as a fertile example of this type is probably part of a frond of the Osmundaceous fern _Todites_. Since this opinion was expressed I have had an opportunity of examining the actual specimen at Padua: the circular patches described by Zigno as sori appear to be irregularities in the matrix and not an original feature.

Brongniart[1471] instituted the genus _Pachypteris_ for some imperfectly preserved English Jurassic fossils from Whitby, which he described as _P. lanceolata_. Specimens have since been described[1472] from the Inferior Oolite rocks of the Yorkshire coast. Brongniart described the pinnules as being without veins or as possessing only a midrib. It is almost certain that the apparent absence of veins in most specimens[1473] is due to the fleshy nature of the segments and that the species _P. lanceolata_ should be transferred to _Dichopteris_.

Krasser[1474] has described a species from Cretaceous rocks of the island of Lesina, off the Dalmatian coast, as _Pachypteris dalmatica_ which is very similar in habit to the English specimens and to Zigno’s _Dichopteris visianica_. One of Krasser’s specimens is practically identical with _Dichopteris lanceolata_ (Brongn.), while in others the small pinnules are replaced in some of the pinnae by a continuous lamina with a few distal serrations. The latter form a link between the _Dichopteris_ and _Thinnfeldia_ type of segment. Krasser gives a full résumé of opinions expressed by other authors in regard to the position of _Pachypteris_ (= _Dichopteris_) and decides in favour of a Cycadean alliance.

[Illustration: FIG. 363. _Dichopteris visianica_, Zigno. (⅓ nat. size. After Zigno.)]

A French Jurassic plant which Saporta[1475] made the type of a new genus _Scleropteris_, and described as _S. Pomelii_, appears to be indistinguishable from _Dichopteris_.

_Dichopteris_, though conveniently retained as a distinct genus, agrees so closely, in the broad and forked rachis and in the fleshy pinnules, with _Thinnfeldia_ that it would seem reasonable to regard the two genera as members of the same group.

Several authors have drawn attention to the striking resemblance in form and venation between the fronds of the Palaeozoic genus _Odontopteris_ and those of _Ctenopteris_ and _Thinnfeldia_. In _Odontopteris_, as in _Neuropteris_, another Palaeozoic genus, the rachis occasionally bifurcates as in _Thinnfeldia_ and _Dichopteris_, and the ultimate segments of some species of _Odontopteris_ (fig. 366, A) are practically identical with those of _Thinnfeldia_ and _Ptilozamites_.

_Odontopteris_ is probably a Pteridosperm. There is no adequate reason for supposing that this group of plants which played a prominent part in the Permo-Carboniferous floras was no longer in existence during the Mesozoic era.

Odontopteris.

Brongniart[1476] instituted the genus _Odontopteris_ for compound fronds from the Coal-Measures characterised by pinnules attached by the whole breadth of the base and traversed by numerous forked veins. _Odontopteris_ is very rare in British Carboniferous rocks and “appears to be restricted to the Middle and Upper Coal-Measures[1477].”

[Illustration: FIG. 364.

A. _Alethopteris lonchitica_ (Schloth.). ½ nat. size. B. _Mariopteris muricata_ (Schloth.). × 2. C. _Odontopteris_ cf. _alpina_ (Presl). ⅗ nat. size. D. _O_. cf. _alpina_. Portion of pinna enlarged.

(A–D. From photographs by Dr Kidston.)]

Fronds large, bipinnate or tripinnate, the main rachis, which may be dichotomously branched, bears long linear pinnae with broadly linear or deltoid pinnules, acute or blunt, attached by the whole of the base; the lower margin of the lamina, which is usually entire and rarely lobed (e.g. _Odontopteris osmundaeformis_)[1478], is often decurrent on the axis of the pinna. The basal pinnule of each pinna is frequently attached by a contracted base, and the lamina may differ in form from that of the normal segments. Pinnules often occur on the main rachis, and in some species the petiole bears modified pinnules which are larger than the ultimate segments of the pinnae and in some cases Cyclopteroid in shape. The pinnules are traversed by numerous dichotomously branched veins; if a midrib is present it dies out in the basal part of the lamina. In some species (genus _Mixoneura_) pinnules of the Neuropteroid type, characterised by a well-defined midrib, occur in association with typical Odontopteroid pinnules on the same pinna.

[Illustration: FIG. 365. _Odontopteris minor_, Brongn. (Rather less than ⅓ nat. size. After Zeiller.) [The pinnules are omitted in the right-hand branch.]]

The species represented in fig. 364, C, D, from the Middle Coal-Measures of Barnsley, Yorkshire, illustrates the form and venation of the _Odontopteris_ type of pinnule. Another species, _O. Reichiana_ Gutb.[1479], is also recorded by Kidston from the Lower Coal-Measures of Lancashire. Some unusually good specimens of the type-species of the genus _Odontopteris minor_, Brongn., have been figured by Zeiller[1480] from the Coal-Measures of Blanzy (fig. 365) which show the dichotomy of the main axis and the occurrence of Aphlebiae on the petiole. The late Dr Weiss[1481] divided _Odontopteris_ into two sections, _Xenopteris_ and _Mixoneura_, the pinnules of the former having the form shown in fig. 364, D; while in species of the latter sub-genus some of the pinnules are identical in form and venation with those of _Neuropteris_ except that they are attached by the whole breadth of the base. Zeiller[1482] employs _Mixoneura_ as a generic designation. In an American species _O. Wortheni_ Lesq.[1483] the pinnules bear numerous hairs like those on some species of _Neuropteris_ (fig. 373, p. 570). The large size of the fronds of _Odontopteris_ suggested to Weiss[1484] that they were borne on the stems of tree-ferns, but Grand’Eury’s[1485] examination of specimens in the Coal-beds of central France led him to picture the plant as bearing a tuft of leaves on a short subterranean stem. Renault and Zeiller[1486], on the other hand, obtained evidence in the Commentry Coal-field of fronds borne on elongated stems which grew on the ground and were supported by stronger plants. Stur[1487] was the first to suggest that _Odontopteris_ should be excluded from the ferns. Grand’Eury’s[1488] supposed fertile pinnules of _Odontopteris_ do not afford any satisfactory evidence of the sporangial nature of the small swellings which he figures at the ends of the veins. This author pointed out several years ago that the petioles of some species of _Odontopteris_ possess the anatomical features of _Myeloxylon_, a type of leaf-stalk which is now known to belong to Pteridosperms. In a recent paper Grand’Eury[1489] records the association of _Odontopteris_ fronds with small seeds (_Odontopterocarpus_), a discovery which leaves little or no doubt as to the Pteridospermic nature of the genus. The fronds of _Odontopteris_ are very similar in habit to those of _Neuropteris_, another Pteridospermic genus.

The similarity between some _Odontopteris_ and _Thinnfeldia_ leaves, to which attention has already been called, is well illustrated by _O. genuina_ Grand’Eury[1490], a pinnule of which is represented in fig. 366, A. _Odontopteris_ is a fairly widespread genus in Upper Carboniferous and Lower Permian rocks, and is recorded also from Triassic strata: it is represented in the Coal-fields of North America and in several parts of Europe[1491].

In some fronds included in _Odontopteris_ the pinnae are characterised by a broad irregularly lobed lamina which also forms a winged border to the rachis. Examples of this form are afforded by _Odontopteris Browni_ Sew.[1492] from the Burghersdorp Series (Triassic?) of Cape Colony, and _O. Fischeri_ described by Brongniart[1493] from the Permian of Russia. The Russian species would perhaps be more appropriately placed in the genus _Callipteris_, as Weiss[1494] suggests; the absence of venation in _O. Browni_ renders generic identification unsatisfactory.

[Illustration: FIG. 366.

A. _Odontopteris genuina_ (Grand’Eury). (× 2⅝. After Renault and Zeiller.) B. _Callipteridium gigas_ (Gutb.). (× 2⅝. After Zeiller.) C. _Callipteris Pellati_ (Zeill.). (× 1¾. After Zeiller.) D. _C. lyratifolia_ (Goepp.). (× 1¾. After Zeiller.)]

Callipteris.

Brongniart[1495] instituted this genus for certain species of supposed ferns previously referred to the genera _Pecopteris_, _Alethopteris_, and _Neuropteris_. _Callipteris_ is a characteristic Permian plant which is almost certainly a Pteridosperm. Zeiller has pointed out that such descriptions of fertile specimens as have been written are unsatisfactory. A few years ago, however, Grand’Eury[1496] recorded the occurrence of seeds in association with Callipteris fronds in the Autun district, and in some cases they were found attached to the pinnae and rachis. The seeds are ovoid or spherical (5–10 mm. broad) and smaller than those of _Neuropteris_. The drawings of fertile segments published by Weiss[1497] afford no indication of reproductive organs. Potonié[1498] figures some pinnules of _Callipteris conferta_ in which the thick lamina is covered with sinuous grooves probably made by some insect larvae: as he suggests, similar markings may have been mistaken for the remains of sori. The occurrence of _Callipteris_ fronds recorded by Weber and Sterzel[1499] in association with _Medullosa_ stems in the Lower Permian of Saxony is in accordance with Grand’Eury’s conclusion.

Fronds reaching 1 metre in length, bipinnate or tripinnate, main rachis frequently exhibiting a combination of dichotomous and pinnate branching. Pinnae linear, usually crowded, decurrent on the rachis; the pinnules on the lower side of the pinnae are continued on to the rachis. Pinnules of the Pecopteroid type, entire or slightly lobed, or of the Sphenopteroid type and more or less deeply dissected (fig. 366 C, D), the lamina of adjacent pinnules concrescent; on the lower pinnae the lamina may be continuous as in an Alethopteris pinnule. A midrib may extend almost to the bluntly rounded apex of the ultimate segments, giving off oblique, simple, or forked veins, the lowest of which arise directly from the rachis; in the Sphenopteroid forms the lateral veins are given off at a more acute angle.

A striking feature of the genus is the occurrence of pinnules on the main rachis, as in _Odontopteris_. Zeiller has wisely extended the application of _Callipteris_ to fronds possessing this character irrespective of the entire or lobed form of the ultimate segments. He found among the numerous examples of the genus obtained from Autun[1500] and Lodève[1501] transitional forms connecting such species as _C. conferta_ (fig. 367) and _C. Pellati_ Zeill. (fig. 366, C) in which the Pecopteroid pinnules are slightly lobed, with _C. lyratifolia_ (Goepp.) (fig. 366, D), _C. flabellifera_[1502] (Weiss), and _C. Bergeroni_ Zeill. characterised by deeply lobed Sphenopteroid segments.

_Callipteris conferta_ (Sternberg)[1503]. Fig. 367.

1723. Scheuchzer, Herb. Diluv. Pl. II., fig. 3.

1826. _Neuropteris conferta_, Sternberg, Flor. Vorwelt, p. 17.

1849. _Callipteris conferta_, Brongniart, Tableau, p. 24.

This polymorphic species (fig. 367) is one of the most characteristic Permian plants. The oval-linear pinnules, attached by the whole base, occur on both pinnae and rachis; this feature, the thick texture of the lamina, and the linear, obliquely set, pinnae render the fronds easily recognisable. The fronds bore seeds.

[Illustration: FIG. 367. _Callipteris conferta_. From the Permian of Aschbach, Rhenish Prussia (British Museum, No. 39052).]

In a recent account of some Permian plants from Germany, Schuster[1504] refers a portion of a frond to _Callipteris conferta_ (Sternberg) var. _polymorpha_ Sterzel, which is characterised by unusually large and polymorphic pinnules. In size and shape the pinnules recall those of _Neuropteridium validum_ Feist.

Callipteridium.

The name _Callipteridium_, created by Weiss[1505] as a sub-genus of _Odontopteris_, is applied by Zeiller and other authors to a few Upper Carboniferous and Permian species characterised by the occurrence of simply pinnate pinnae on the main rachis between the bipinnate primary pinnae. Single pinnules are borne directly on the rachis of the primary pinnae between the pinnate branches. The form and venation of a typical pinnule are shown in fig. 366, B. _Callipteridium pteridium_, originally recorded by Schlotheim as _Filicites pteridius_[1506], has been fully described by Renault and Zeiller from unusually large specimens found in the Commentry Coal-field[1507]. This species illustrates the peculiar morphological features of the genus. The main rachis of the tripinnate fronds, several metres long, shows a combination of dichotomous and pinnate branching; from the zigzag and forked axis are given off bipinnate pinnae and, between these, shorter pinnate branches. The pinnules closely resemble those of _Callipteris conferta_ but reach a greater length; the pinnules borne on the rachises of the lateral branches differ from the others in their broader base and more triangular lamina.

No fertile specimens have been found. It is probable that _Callipteridium_ was not a true fern, and that White[1508] is correct in including it among the Pteridosperms.

Archaeopteris.

In 1852 Forbes[1509] published a brief description of some supposed fern fronds, found by the Geological Surveyors of Ireland in Upper Devonian rocks of Kilkenny, under the name _Cyclopteris hibernica_. The Irish specimens were more fully described by Baily[1510] in 1858. Fronds of the same type were referred by other authors to _Cyclopteris_, _Adiantites_ or _Noeggerathia_, until Schimper[1511] proposed the generic name _Palaeopteris_ on the ground that the fronds described by Forbes and Baily are distinguished by the nature of their fertile pinnae from the sterile leaves included in Brongniart’s provisional genus _Cyclopteris_. The earlier use of _Palaeopteris_ by Geinitz for an entirely different plant led Dawson[1512] to institute the genus _Archaeopteris_. The genus _Archaeopteris_ may be defined as follows:

Fronds bipinnate, reaching a considerable length (90 cm.); the stout rachis bears long linear pinnae; sterile pinnules obovate or cuneate with an entire, lobed, fimbriate, or laciniate lamina traversed by divergent dichotomously branched veins. The fertile pinnae usually occur on the lower part of the rachis; pinnules with a much reduced lamina bear numerous fusiform or oval exannulate sporangia (fig. 369, A, E, H), sessile or shortly stalked, singly, or in groups of two or three. The base of the petiole is characterised by a pair of partially adnate stipules (fig. 369, C, D), and single pinnules or scales occur in some species on the rachis between the pinnae and on the petiole.

[Illustration: FIG. 368. _Archaeopteris hibernica_. (From a specimen in the Science and Art Museum, Dublin. Rather less than ⅙ nat. size.)]

_Archaeopteris hibernica_ (Forbes). Figs. 368, 369, A–C.

The specimen from Kilkenny represented in fig. 368 has a length of over 80 cm. The upper pinnae bear numerous imbricate obovate pinnules (fig. 369, A, B) with an entire or very slightly fimbriate margin, while on the shorter lower pinnae the ultimate segments are reduced to a slender axis bearing numerous fusiform sporangia, 2–3 mm. in length. Kidston[1513] has pointed out that sporangia occasionally occur on the edge of ordinary pinnules, and he first recognised the stipular nature of the scale-like appendages which Baily noticed on the swollen petiole base (5 cm. broad) of the Irish species (fig. 369, C). Restorations of _Archaeopteris hibernica_ have been figured by Baily[1514] and by Carruthers[1515], but the description of the fertile pinnae by the latter author requires modification in the light of Kidston’s description of the Dublin specimens.

• • • • •

_Archaeopteris_ is recorded from Upper Devonian rocks of the South of Ireland, Belgium, Germany, Southern Russia, Bear Island, and Ellesmere Land in the Arctic regions, Canada, Pennsylvania, and elsewhere. Many of the specimens described under different names bear a close resemblance, which in some cases probably amounts to specific identity, to _A. hibernica_. _A. Jacksoni_ originally described by Dawson[1516] and more recently by Smith and White[1517] from Devonian rocks of Maine, the Canadian type _A. gaspiensis_ Daws., and some species figured by Lesquereux[1518] from Pennsylvania, are examples of forms which present a striking similarity in habit to the Irish species. The Belgian Devonian fossils named by Crépin[1519] _Palaeopteris hibernica_ var. _minor_ are regarded by him as probably identical with Goeppert’s species _Cyclopteris Roemeriana_ from the neighbourhood of Aachen. Heer recorded _Archaeopteris Roemeriana_ from Upper Devonian beds in Bear Island, and Nathorst[1520], who has published a more complete account of the Arctic forms, draws attention to the resemblance of some of them to _A. hibernica_. A species described by Schmalhausen[1521] from the Upper Devonian of Southern Russia as _A. archetypus_ (fig. 369, D) appears to differ from _A. hibernica_ in the slightly less reduced lamina of the fertile segments. This species has been more adequately illustrated by Nathorst[1522] from material collected in Ellesmere Land: he is unable to confirm Schmalhausen’s statement that the pinnae are spirally disposed.

The species _A. fimbriata_ (fig. 369, G) described by Nathorst from Bear Island is characterised by the more deeply dissected lamina of the sterile pinnules. In _A. fissilis_ Schmal. from Russia and Ellesmere Land the lamina (fig. 369, E, F) is cut up into filiform segments: a fertile pinnule of this species is represented in fig. 369, E.

Some sterile impressions figured by Krasser[1523] from Palaeozoic strata (Lower Carboniferous or Upper Devonian?) in the province of Nanshan in China as _Noeggerathia acuminifissa_ are considered by Zeiller[1524] to be portions of an _Archaeopteris_ or _Rhacopteris_ frond. The resemblance to the former genus is however by no means close enough to warrant a reference to _Archaeopteris_. The sterile specimens described by Stur[1525] from the Culm of Altendorf as species of _Archaeopteris_ are probably not generically identical with the Irish and Arctic species. The dichotomous branching of the rachis in _A. Tschermaki_ and _A. Dawsoni_ is a feature unknown in _Archaeopteris_. In the absence of fertile pinnae the separation of _Archaeopteris_ from _Rhacopteris_ is by no means easy.

[Illustration: FIG. 369.

A. _Archaeopteris hibernica._ Fertile pinna. Dublin Geological Survey Museum. (Reduced. After Kidston.) B. _A. hibernica._ Pinnule. (Slightly enlarged. After Carruthers.) C. _A. hibernica._ Base of petiole. (Dublin Museum. After Kidston.) D. _A. archetypus._ Base of petiole: Ellesmere Land. (After Nathorst. ⅚ nat. size.) E. _A. fissilis._ Sporangia. (Slightly enlarged. After Schmalhausen.) F. _A. fissilis._ Sterile pinnule. Ellesmere Land. (Slightly enlarged. After Nathorst.) G. _A. fimbriata._ Bear Island. (After Nathorst. ⅚ nat. size.) H. _Archaeopteris sp._ Ellesmere Land. (After Nathorst. ⅚ nat. size.)]

_Archaeopteris_ was regarded by Carruthers as a fern closely allied to recent species of Hymenophyllaceae, but this conclusion was based upon an interpretation of the fertile segments which Kidston[1526] has shown to be incorrect. The latter author regarded the presence of stipules and the structure of the exannulate sporangia as evidence of a Marattiaceous alliance. In a later reference to _Archaeopteris_, Kidston expresses the opinion that the genus is not a true fern but a member of the Cycadofilices or Pteridosperms, a view shared by Grand’Eury[1527] and doubtless by many other palaeobotanists. The sporangia of _Archaeopteris_ appear to be of the same type as those of _Dactylotheca_ (fig. 290, E, p. 399). Schmalhausen gave expression to his disagreement with Nathorst and other authors who referred _Archaeopteris_ to the Marattiaceae by proposing the distinctive group-name Archaeopterideae.

There can be little doubt that the reproductive organs of _Archaeopteris_ so far discovered are microsporangia, and that the plant bore seeds. The sporangia are larger than those of any known fern and, as Kidston points out, they are similar to those of _Crossotheca_ which he has shown to be microsporangia of the Pteridosperm _Lyginodendron_. The presence of stipules in _Archaeopteris hibernica_, _A. fimbriata_, _A. archetypus_ (fig. 369, D) and probably throughout the genus does not materially affect the question of taxonomic position. Stipules are a characteristic feature of Marattiaceae and, in a reduced form, of Osmundaceae, but similar appendages are borne at the base of the petiole of the Cycad _Ceratozamia_. The occurrence of Aphlebiae on the rachis of _Archaeopteris_ is a feature shared by the fronds of _Neuropteris_ and other Pteridosperms.

Neuropteris.

The fronds for which Brongniart[1528] created this genus, though suspected by Stur in 1883 as wrongly classed among the ferns, have only recently been shown to be the leaves of Pteridosperms. As yet only one case is recorded in which

_Neuropteris_ pinnae occur in organic connexion with seeds[1529], but it is almost certain that the genus as a whole must be placed in this generalised group. Renault[1530] pointed out that the petioles of Neuropteris fronds from Autun had the anatomical features of _Myeloxylon_ (petiole of _Medullosa_). Since Kidston’s important discovery of seed-bearing pinnae of _N. heterophylla_, Grand’Eury[1531] has recorded the association of Neuropteris fronds with seeds in French Coal-fields. By some of the older authors _Neuropteris_ was compared with _Osmunda_ because of a similarity in venation. In the frequent dichotomy of the frond and in the occurrence of pinnules on the rachis, _Neuropteris_ closely resembles _Odontopteris_[1532]: there can be little doubt as to the close relationship of the Pteridosperms possessing these two types of foliage. _Neuropteris_ may be defined as follows:

Fronds reaching a considerable size, probably in soma cases a length of 10 metres[1533]; bi- or tri-pinnate; the rachis may be dichotomously branched (figs. 354, D; 370); both rachis and petiole bear single pinnules, those on the latter frequently differ from the normal leaflets in their larger Cyclopteroid laminae (fig. 370). Pinnules entire, rarely slightly lobed, broadly linear, attached by a small portion of the base, which is usually more or less cordate. In _N. Grangeri_ Brongn. the pinnules are attached by a short pedicel[1534]. The midrib always dies out before reaching the blunt or pointed apex of the lamina and gives off at an acute angle numerous secondary veins characterised by their arched course and repeated forking.

[Illustration: FIG. 370. _Neuropteris_ frond with _Cyclopteris_ leaflets. English Coal-Measures. (From a block given to me by Mr Carruthers. A.C.S.)]

Potonié describes the secondary veins of the pinnules of _Neuropteris pseudogigantea_[1535] as occasionally anastomosing, a feature which may be regarded as a step towards the reticulate venation of the closely allied genus _Linopteris_.

Renault[1536] described some petrified pinnules of _Neuropteris_ in which the mesophyll shows a differentiation into upper palisade tissue and lacunar tissue below; the lower epidermis is infolded at intervals where grooves (probably stomatal) occur like those on the leaves of an Oleander (_Nerium oleander_).

The rachises of Neuropteris fronds are described by Grand’Eury under the generic name _Aulacopteris_[1537].

_Neuropteris heterophylla_, Brongniart[1538]. Figs. 354, E; 371.

This species is characteristic of the Lower Coal-Measures of Britain; it occurs also in the Middle Coal-Measures and is a common type in Upper Carboniferous rocks in various parts of the world. The fronds are large and tripinnate, the rachis is often dichotomously branched and Cyclopteroid pinnules may occur on the petiole. The pinnules, 5–20 mm. in length and 3–8 mm. broad, have a rounded apex (fig. 354, E, p. 535).

[Illustration: FIG. 371. _Neuropteris heterophylla._ From a specimen in the Manchester Museum. ½ nat. size. M.S.]

As shown in fig. 371 which represents a primary pinna, the small pinnules on the lower branches are gradually replaced in the upper portion of the specimen by falcate segments.

_Neuropteris macrophylla_, Brongniart[1539]. Figs. 354, D, D′; 372.

The rachis of the large fronds of this species illustrates the dichotomous habit of many Neuropteris fronds, also the occurrence on the petiole of large Cyclopteroid pinnules (cf. fig. 370). The small piece of a pinna reproduced in fig. 372 shows the slender attachment of the segments, the blunt apex, and the Neuropteroid venation. Single pinnules of this species may be distinguished from those of _N. Scheuchzeri_ by the blunter apex, the absence of the pair of small Cyclopteroid pinnules on the same branch and by the absence of hairs. _N. macrophylla_ is characteristic of the Upper Coal-Measures of Britain.

[Illustration: FIG. 372. _Neuropteris macrophylla_, Brongn. From a photograph by Mr Hemingway.]

_Neuropteris Scheuchzeri_, Hoffmann. Figs. 354, F; 373.

Fragments of this well-known Coal-Measure species were figured by Scheuchzer in his _Herbarium Diluvianum_[1540] as _Lithosmunda minor_, and by Lhywd (Luidius[1541]) as _Phyllites mineralis_ as early as 1760. _Neuropteris Scheuchzeri_, so named by Hoffmann in 1826, is a type which many authors have described under different names. Lesquereux[1542] figured it as _N. hirsuta_ from the Coal-fields of Pennsylvania, and under the same name it is recorded by Fontaine and White[1543] from Permian rocks of Virginia. The oval patches on the surface of a pinnule described by these authors as sori are certainly not of that nature. The same species is described by Bunbury[1544] from Nova Scotia as _N. cordata_ Brongn. var. _angustifolia_. For a full synonymy of the species reference should be made to lists published by Kidston[1545], White[1546], and Zeiller[1547].

[Illustration: FIG. 373. _Neuropteris Scheuchzeri._ From a specimen (v. 2009) in the British Museum. ¾ nat. size.]

The large tripinnate fronds are characterised by the long linear- or oval-lanceolate pinnules (fig. 373)[1548] with a pointed apex and numerous bristle-like hairs on the lamina; two much smaller Cyclopteroid segments occur at the base of the pinnae which are terminated by the linear leaflets (fig. 354, F, p. 535).

_Neuropteris Scheuchzeri_ is characteristic of the Upper and Middle Coal-Measures of Britain and is recorded from several localities in North America and the Continent. Zalessky[1549] has recently recorded the species from the Coal-Measures of Donetz. The frequent occurrence of detached pinnules points to a caducous habit. Even single leaflets can, however, be identified by their large size, the pointed apex, and hairy lamina. The hairs are preserved as fine oblique lines simulating veins; they were so described by Roemer[1550] who took them for cross-connexions between the secondary veins and referred the pinnules to Gutbier’s genus _Dictyopteris_.

Another example of _Neuropteris_ with hairy pinnules is described from the Commentry Coal-field by Renault and Zeiller as _N. horrida_[1551]. The oval-linear, bluntly rounded, pinnules are characterised by a median band of hairs on each surface and a narrower strip at the edge of the lamina.

Cyclopteris.

This generic name was created by Brongniart in 1828[1552] for specimens which he believed to be complete single leaves of orbicular or reniform shape similar to those of _Trichomanes reniforme_. The lamina is traversed by numerous dichotomously branched veins which spread from the centre of the base.

It was suspected by Lindley and Hutton[1553] that certain Cyclopteris leaves belonged to the frond of a species of _Neuropteris_, and some years later Lesquereux[1554] concluded that Brongniart’s genus was founded on orbicular leaflets of _Neuropteris_. In 1869 Roehl[1555] figured a specimen of _Neuropteris_ bearing Cyclopteroid pinnules on its rachis. It is now universally admitted that _Cyclopteris_ is not a distinct genus and that the specimens so named were borne as modified pinnules on the main rachis of _Neuropteris_ and _Odontopteris_. It is, however, convenient to retain the name for detached leaflets which cannot be referred to the fronds on which they were borne. A specimen found by Mr Hemingway in the Upper Coal-Measures of Yorkshire and described in 1888[1556] affords a striking example of the large size attained by what was probably a frond of _Neuropteris_. The piece of main rachis reached a length of over 120 cm. and bore five pairs of Cyclopteris pinnules, some of which were 7 cm. long and 5 cm. broad. The complete frond must have reached a length of at least 4 metres. Fig. 370 shows some typical Cyclopteroid leaflets on the petiole of a _Neuropteris_ frond.

Linopteris.

The Upper Palaeozoic fronds included in this genus are more familiar as species of _Dictyopteris_. Potonié[1557] has, however, pointed out that the creation of this name by Lamouroux in 1809 for a genus of Brown Algae which is still retained, makes it advisable to fall back upon the designation _Linopteris_. Gutbier[1558] proposed the genus _Dictyopteris_ in 1835: _Linopteris_ was first used by Presl[1559] in 1838. The fronds so named are identical with species of _Neuropteris_ except in the anastomosis of the secondary veins; _Linopteris_ bears to _Neuropteris_ the same relation as _Lonchopteris_ bears to _Alethopteris_. As in _Neuropteris_, Cyclopteroid pinnules occur on the petioles of _Linopteris_, but the veins form a fine reticulum. Grand’Eury[1560] records the association of _Linopteris Brongniarti_ with seeds belonging to the genus _Hexagonocarpon_, a fact which points to the Pteridosperm nature of the foliage.

Some fertile pinnules of _Linopteris Schutzei_ (Roemer) are described by Zeiller[1561] from Autun as bearing on the under surface of the lamina two rows of long and pointed sporangia, probably united in groups. The presumption is that these are microsporangia.

Fig. 374 is a reproduction of a careful drawing, originally published by Zeiller[1562], of a pinnule of the type-specimen of Gutbier’s species _Linopteris neuropteroides_. This species differs from _Linopteris obliqua_, instituted by Bunbury[1563] for specimens obtained by Lyell[1564] from the Coal-Measures of Nova Scotia, in the smaller size of the meshes. _Linopteris obliqua_ occurs in the Upper and Middle Coal-Measures of Britain; it is recorded by Zeiller from Asia Minor, by Lesquereux[1565] from Pennsylvania, and by other authors from several European localities. The pinnules frequently occur detached from the frond and like those of some species of _Neuropteris_ were caducous. _Linopteris_ is rare in British strata.

[Illustration: FIG. 374. _Linopteris neuropteroides_, Gutb. (Pinnule of type-specimen. Enlarged. After Zeiller.)]

Alethopteris.

The name _Alethopteris_, instituted by Sternberg[1566], is applied to compound fronds often reaching a considerable size, exhibiting the following features:

The linear pinnules are attached by the whole breadth of the base, with the lower edge of the lamina decurrent and usually continuous with that of the next pinnule (figs. 290, A, p. 399; 375). The ultimate segments are entire, with an acute or rounded apex and often characterised by a fairly thick lamina convex on the upper surface. From a prominent midrib, continued to the apex of the pinnule, numerous simple and forked secondary veins are given off at a wide angle, the decurrent portion of the lamina being supplied by veins direct from the axis of the pinna. In the upper part of a frond or primary pinna the pinnules may be replaced by a continuous, lobed, or entire simple lamina. The main rachis occasionally exhibits dichotomous branching, but the fronds are for the most part constructed on the pinnate plan. Single Cyclopteroid pinnules[1567] occur on the petiole of some species of the genus.

In certain species of _Alethopteris_ the pinnules appear to have been deciduous as in _Didymochlaena_ among recent ferns[1568]. A piece of cuticle from the upper surface of a pinnule of _Alethopteris Grandini_ (Brongn.) figured by Zeiller[1569] shows very clearly the polygonal form and straight walls of most of the epidermal cells, those above the veins being almost rectangular. The position of the sunken stomata is revealed by small circular spaces surrounded by a circle of cells.

The absence of fertile specimens of this common genus of Upper Carboniferous plants led Stur[1570] to exclude it from the ferns. Although no seeds have so far been found in organic connexion with an Alethopteris frond, it is certain that some species, probably all, represent the foliage of Pteridosperms. Renault was the first to describe petrified specimens of _Alethopteris_ fronds exhibiting the anatomical structure of _Myeloxylon_ (leaf-axis of _Medullosa_). The calcareous nodules from English Coal-seams contain numerous fragments of the Myeloxylon type of rachis bearing Alethopteroid pinnules.

The constant association of the fronds of _Alethopteris lonchitica_ and _Trigonocarpon_ seeds noticed by Mr Hemingway in the Coal-Measures of Yorkshire led him to regard the species as seed-bearing: it has since been recognised as the foliage of the Pteridosperm _Medullosa anglica_[1571].

Grand’Eury[1572] has recorded the association in French Coal-fields of species of _Alethopteris_ with _Trigonocarpon_ and _Pachytesta_ seeds.

_Alethopteris lonchitica_ (Schlotheim)[1573]. Figs. 364, A; 290, A.

This species, described by Schlotheim in 1820 as _Filicites lonchiticus_ and previously figured by Scheuchzer[1574], is abundant in the Middle and Lower Coal-Measures of Britain[1575]. It is characterised by large tripinnate fronds, probably quadripinnate in the lower part, bearing primary pinnae of a more or less triangular form divided into pinnate branches replaced in the apical region by linear segments. The pinnules, 8–30 mm. long and 3–5 broad, are linear- or oval-lanceolate with an obtuse apex; the upper margin of the lamina is slightly contracted at the base, while the lower edge is decurrent.

[Illustration: FIG. 375. _Alethopteris Serlii_ (Brongn.). From a specimen in the York Museum. ¾ nat. size.]

_Alethopteris Serlii_ (Brongniart)[1576]. Fig. 375.

This species, figured by Parkinson in 1811, closely resembles _A. lonchitica_, but is distinguished by the more crowded and relatively longer pinnules which are joined to one another by a narrow connecting lamina (Fig. 375). The secondary veins in _A. Serlii_ are rather finer and more numerous. Grand’Eury[1577] records the association of the seed _Pachytesta_ with fronds of this species in the Coal-Measures of St Étienne.

_A. Serlii_ is very abundant in the Upper Coal-Measures but rare in the Middle Coal-Measures of Britain[1578].

Lonchopteris.

This name was proposed by Brongniart[1579] for sterile fronds from Upper Carboniferous rocks which are practically identical with species of _Alethopteris_, but differ in the reticulate venation of the pinnules. It has been pointed out in a previous chapter[1580] that _Lonchopteris_ is usually used for Palaeozoic species, the Wealden leaves, which were placed in this genus by Brongniart, being transferred to _Weichselia_.

There can be little doubt as to the close relationship of _Lonchopteris_ with _Alethopteris_: both may be referred to the Pteridosperms. _Lonchopteris rugosa_ Brongn.[1581] (fig. 290, B, p. 399) and _L. Bricei_ Brongn., both British species, are fairly common in Upper Carboniferous strata. In _L. rugosa_, a Middle Coal-Measures species, the anastomosing secondary veins form polygonal meshes (fig. 290, B, p. 399) smaller than those of _L. Bricei_.

Pecopteris.

Reference has already been made to this genus in the chapter on Marattiales, so far as regards certain species of fertile fronds the sporangia of which resemble those of recent Marattiaceae. It is, however, by no means safe to assume that such Pecopteris fronds were borne on stems having the anatomical characters of ferns. The sporangia in some at least of the species may have contained microspores. In one Upper Carboniferous species usually referred to Pecopteris, _P. Pluckeneti_, Schlot., Grand’Eury[1582] has recorded the occurrence of seeds on the pinnules of the ordinary fronds. This species will be referred to in Volume III. The substitution of such generic names as _Ptychocarpus_, _Asterotheca_, _Hawlea_, _Dactylotheca_ and others for the purely provisional designation _Pecopteris_ indicates a step towards a conclusion as to natural affinity. The probability is that _Pecopteris_, as applied to Palaeozoic species, in many cases stands for the compound fronds of true ferns, but the possibility of the inclusion of those of Pteridosperms in the same category is by no means excluded. The designation _Pecopteris_ may conveniently be retained for sterile bipinnate, tripinnate, or quadripinnate fronds bearing pinnules having the following characteristics:

Lamina short, attached to the rachis by the whole of the base and at a wide angle, with the edges parallel or slightly converging towards the usually blunt apex; adjacent pinnules may be continuous basally by a narrow lamina. A well-marked midrib extends to the apex and gives off simple or forked lateral veins almost at right angles (fig. 352, D, p. 529).

Hydathodes like those on the leaflets of _Polypodium vulgare_ and other recent ferns[1583] are occasionally seen at the ends of the lateral veins of Pecopteris pinnules.

In addition to the examples of Palaeozoic fronds with the _Pecopteris_ form of pinnule referred to in