Chapter XXXIX: Cycadophytan Fronds (2)

This Wealden species, first described by Dunker as _Cyclopteris Klipsteinii_[1560], is remarkable for the large pinnae. The rachis is fairly stout; the broadly oval or oblong pinnae vary considerably in size and in the relation of breadth to length, in rare cases reaching a length of over 8 cm. and a breadth of 2·4 cm.; apex obtuse, base slightly auriculate and asymmetrical; veins numerous, radiating from the point of attachment to the margin of the lamina. The occurrence of finer lines between the more prominent veins may indicate the presence of hypodermal stereome strands. Fig. 608 illustrates the striking variation in the size of the pinnae on a single frond and their attachment to the upper face of the rachis. In the breadth of the segments _O. Klipsteinii_ resembles _O. Beani_ (Lind. and Hutt.), _O. decorus_ Sap.[1561], _O. lagotis_ Brongn.[1562] and two species from South Russia described by Thomas[1563] as _O. Izuimensis_ and _O. giganteus_. The pinnae of _O. giganteus_ exceed 10 cm. in length and 3 cm. in breadth, thus surpassing the largest segments of _O. Klipsteinii_. Some pinnae from the Jurassic flora of Oregon made by Fontaine the type of a new species, _O. oregonensis_[1564], may be fragments of _O. Klipsteinii_. Nathorst[1565] records the occurrence in Lower Cretaceous or Wealden beds in Spitzbergen of Cycadean leaflets very like those of _O. Klipsteinii_.

_Otozamites Goeppertianus_ (Dunker).

This Wealden species, named by Dunker[1566] _Pterophyllum Goeppertianum_, agrees in habit with some of those to which reference is made under _O. Bechei, e.g. O. linearis_ Halle, and represents a type of the genus with unusually narrow pinnae (fig. 603, A). The auriculate form of the lamina is feebly developed; the linear-lanceolate pinnae are occasionally falcate and have acute apices; as in many other species they were apparently deciduous. It is by no means easy to distinguish some of these fronds from specimens included in _Ptilophyllum pecten_.

=DICTYOZAMITES.= Oldham.

This generic name was instituted[1567] for pinnate fronds from the Rajmahal series of India, assigned by Feistmantel to a Lower Jurassic horizon, but probably nearer in age to the Middle Jurassic series. Morris, joint author with Oldham of the Memoir on the Rajmahal plants, adopted the name _Dictyopteris_. _Dictyozamites_ agrees very closely with _Otozamites_ but is readily distinguished by the anastomosing veins (fig. 609), while the absence of a midrib differentiates it from the Palaeozoic genus _Dictyopteris_. The genus is recorded also from Jurassic strata in England, Bornholm, Japan[1568], Korea[1569], and from a locality 60 nautical miles N.W. of Cape Horn in Tierra del Fuego[1570]: the specimens from these localities differ only in unimportant details from the Indian type. _Dictyozamites_ is confined to Jurassic floras and appears to be especially characteristic of Middle Jurassic floras. In India[1571] fronds occur in close association with stems of the _Bucklandia_ type and, although there is no proof of any connexion with stems or flowers, it is probable that the fronds of this generic type were borne on stems similar to those of _Bucklandia_ and that the flowers were constructed on the _Williamsonia_ plan.

_Dictyozamites falcatus_ (Morris).

Morris[1572] described this Rajmahal species under the names _Dictyopteris falcata_ and _D. falcata_ var. _obtusa_; the specimens were included by Feistmantel under the designation _Dictyozamites indicus_, the original term _falcata_ being discarded without adequate reason. An examination of several of the figured fronds enables me to confirm the accuracy of the published drawings and to extend the description in a few particulars. Fronds pinnate of the habit of _Otozamites_; pinnae comparatively thick, broadly linear, alternate, varying considerably in size and in the form of the apex which may be obtuse or acute. The pinnae are attached by the middle part of the lamina only; the upper edge of the base is slightly rounded or auriculate; the lower angle is generally more definitely lobed. The imbricate bases completely cover the upper face of the comparatively slender rachis. The longest pinna seen on an Indian frond is 6 cm. with a breadth of 2 cm. Some of the pinnae on magnification exhibit a finely tuberculate appearance, due no doubt to the presence of papillae on the epidermal cells like those on the pinnae of English and Bornholm specimens. This species is recorded by Yokoyama[1573] from Japan as _D. falcatus_ var. _distans_, and a similar form, referred by him to a distinct species, _D. grossinervis_, may be more appropriately named _D. falcatus_ var. _grossinervis_[1574]. The Indian type occurs also in Jurassic rocks of Korea, and Halle has discovered some _Dictyozamites_ leaves in Tierra del Fuego[1575] which he describes as _Dictyozamites_ sp. _cf._ _D. falcatus_: this record is of special interest from a phytogeographical point of view.

_Dictyozamites Johnstrupi_ Nathorst.

This species[1576], from rocks usually spoken of as Liassic but not improbably Middle Jurassic in age, differs from _D. falcatus_ in the slightly more falcate form of the pinnae and in the more strongly auriculate upper angle of the base of the lamina. The stomata[1577] are confined to the lower epidermis and the strongly cuticularised guard-cells frequently lie at right-angles to the course of the veins. The epidermal cells have very sinuous walls (fig. 609, C) and in the middle of each is a prominent papilla.

_Dictyozamites Hawelli_ Seward.

This Middle Jurassic type from Marske[1578], Yorkshire, differs from _D. falcatus_ in the relatively broader segments, their straighter form (fig. 609, B), and in the attachment to the rachis being slightly below the middle of the pinna base. Fig. 609, A, shows the base of a pinna and an oval scar similar to those on the rachis of some recent Cycads (_cf._ fig. 387). The epidermis is like that in _D. Johnstrupi_ and as in that species the stomata are confined to the lower surface. There are approximately 120 stomata per square millimetre; each with two subsidiary cells (fig. 609, C) of elongated form, and the guard-cells have small thickened outgrowths or papillae as in _D. Johnstrupi_.

The epidermal features are described under _D. Johnstrupi_ and _D. Hawelli_ (fig. 609, C): a fuller account of those in the latter species will be found in the paper by Mr Thomas and Miss Bancroft.

=PTEROPHYLLUM.= Brongniart.

The name _Pterophyllum_ was first applied by Brongniart[1579] to some fronds from the Lias of Höör, which he named _P. majus_ and _P. minus_, species subsequently removed by Nathorst[1580] to Schimper’s genus _Anomozamites_. Brongniart[1581] defined _Pterophyllum_ fronds, _e.g._ _P. Jaegeri_ (fig. 610), as pinnate, bearing pinnules of almost equal breadth attached by the whole width of the base and with a truncate apex; veins slender, equal, simple and slightly arched. There has been considerable confusion and laxity in regard to the application of the name _Pterophyllum_ and in many cases no clear distinction has been recognised between this genus and _Nilssonia_. In _Nilssonia_ the distinctive feature is the complete absence of any rachis uncovered by the lamina on the upper face of well-preserved specimens, while in _Pterophyllum_ the continuity of the lamina is broken by a greater or less breadth of rachis in the middle line of the frond; the lamina does not cover the rachis but is attached laterally, or at least the two laminae of the frond, whether entire or deeply dissected, do not meet in the middle of the rachis. A specimen from the Cretaceous of Greenland described by Heer as _Pterophyllum concinnum_[1582] and now in the Stockholm Museum is probably a piece of a _Nilssonia_; the rachis is not exposed on the surface of the frond. In _Nilssonia_ the veins are with few exceptions simple; in _Pterophyllum_ they are often branched especially near their origin from the rachis: in _Nilssonia_ the segments are of unequal breadth; in _Pterophyllum_ they are usually equal. It has been the practice of several authors to follow Schimper[1583] in the employment of the generic name _Anomozamites_ for fronds with a more or less entire or irregularly pinnatisect lamina which bear a very close resemblance to _Nilssonia_ except that a portion of the rachis is exposed on the upper face. Potonié[1584] used _Pterophyllum_ in a wider sense including both fronds with equal pinnae and those of the _Anomozamites_ type: this more extended use of _Pterophyllum_ is adopted by Zeiller[1585] who prefers to retain _Anomozamites_ only as a sub-genus. It is in this sense that the following definition is framed.

Fronds pinnate; pinnae linear, attached by the whole base, which may be enlarged; the apex is truncate, rounded, or occasionally pointed; the veins are simple or dichotomously branched and parallel to the edge of the lamina. In some fronds (sub-genus _Anomozamites_) the segments are unequal (fig. 615), short, broad and truncate, and the lamina may be entire or divided into a few very unequal segments. The surface of the rachis is never completely covered by the lamina on the upper face of the frond and is often characterised by transverse wrinklings, possibly due to the presence of ramental scales.

Some interesting xerophilous features have recently been described by Halle[1586] in the lamina of _Pterophyllum (Anomozamites) marginatum_, a Rhaetic species figured by Schenk and Nathorst from Franconia and Scania. The pinnae were thick and succulent. Stomata are confined to the lower surface and the edges of the upper face of the lamina form a rounded curve causing the thick upper cuticle to abut on the thinner stomatiferous lower cuticle, thus producing in impressions the appearance of thickened margins.

There is no satisfactory evidence as to the nature of the reproductive organs or stems of the plants which bore fronds of the type represented by _P. Jaegeri_ (fig. 610) and other forms with equal segments. A stem referred by Heer[1587] and by Leuthardt[1588] to _Pterophyllum_ was not found in connexion with leaves, and there is the same absence of any convincing evidence in the case of the imperfect specimens from the Keuper of Basel believed by Leuthardt to be male and female inflorescences. On the other hand leaves of _Anomozamites_ are known to have been borne on comparatively slender stems with dichasial branching, and the reproductive shoots are of the same general type as those known as _Bennettites_. This discovery is due to Nathorst who founded the genus _Wielandiella_[1589] on fertile stems with _Anomozamites_ fronds. Mr Thomas[1590] has recently obtained evidence from Yorkshire Jurassic material pointing to a similar connexion between _Anomozamites_ fronds and _Wielandiella_ stems. _Pterophyllum_ is further distinguished from _Nilssonia_ by the folded walls of the epidermal cells and by the presence of two crescentic subsidiary cells (fig. 611, A) instead of the ring of cells which surrounds the guard-cells in _Nilssonia_ (fig. 611, B). Schenk[1591] figured a few pieces of cuticle from fronds referred to _Pterophyllum_ in which the walls are more or less sinuous, but the cells of _Pterophyllum crassinerve_ Goepp.[1592] appear to have straight walls: this species is, however, probably a _Nilssonia_. The stoma represented in fig. 611, A, is from the lower epidermis of _Pterophyllum_ (_Anomozamites_) _Nilssoni_ (Phill.)[1593].

_Pterophyllum_ extends from Upper Carboniferous to Lower Cretaceous strata and is especially characteristic of Keuper and Rhaetic floras. A possible representative of the sub-genus _Anomozamites_ is described by Ettingshausen from Tertiary beds in New South Wales as _Anomozamites Muelleri_[1594].

_Pterophyllum Fayoli_ Renault and Zeiller.

This species[1595] was founded on a large frond from the Commentry coalfield with a stout rachis bearing linear pinnae, attached along a narrow groove on its outer edge, reaching a length of 12 cm. and a breadth of 1 cm.; adjacent pinnae are united at the base. The apices are pointed and there are 10–12 unbranched veins in the lamina. Fig. 612 shows a small piece of the large specimen in the Natural History Museum, Paris.

_Pterophyllum_ sp. Arber.

The only representative of a Carboniferous frond of Cycadean habit discovered in Britain is that recorded by Arber[1596] from Westphalian strata at a depth of 1834 ft at Barfreston in Kent. A fairly stout rachis bears incomplete pinnae the longest of which is slightly more than 1 cm. in length and 1–1·5 cm. broad; each segment, very slightly contracted at the base, has 3–4 occasionally forked veins. Arber compares the fragments with _Pterophyllum blechnoides_ Sand. from Germany[1597].

_Pterophyllum Cambryi_ Renault.

This Permian species from Autun[1598] is similar to _P. Fayoli_, but differs in the more slender rachis and in the finer venation of the linear, acute, pinnae. The pinnae in Renault’s specimen reach a length of 4·8 cm. and are from 3·5–4 mm. broad; they are slightly confluent at the base and the veins occasionally fork.

Among other Palaeozoic species are _Pterophyllum Grand’Euryanum_ Sap. and Mar.[1599] discovered by Grand’Eury in the Coal Measures of France, _P. blechnoides_ Sand.[1600] from the Upper Coal Measures of Oppenau and recorded by Geinitz[1601] from the Middle Permian of Germany, _P. Cottaeanum_ Gutb.[1602], a similar type, also from Permian rocks, but with coarser venation. The specimens figured by Geinitz as _P. blechnoides_ and _P. Cottaeanum_ are in the Dresden Museum: the former species is represented by a good impression on shale which shows the generic characters very clearly.

_Pterophyllum Jaegeri_ Brongniart.

Brongniart[1603] founded this species (fig. 610) on material from the Keuper of Stuttgart. The fronds are characterised by the relatively narrow parallel-sided pinnae with rounded or truncate apices and little or no basal contraction; the pinnae may be contiguous or separate. There are 14–16 veins in each pinna. Leuthardt[1604], who figures several examples of this species from Keuper strata at Basel, speaks of the breadth-index of the pinnae as 12, a term employed to denote the relation of the breadth to the length of a segment. _Pterophyllum longifolium_[1605] is a very similar Keuper type: in this species the pinnae are rather shorter and broader than in _P. Jaegeri_ and contracted at the base; the apex is truncate or obtuse. The differences between these species is, however, very trifling. The imperfectly preserved fossils figured by Leuthardt[1606] as the inflorescences of _Pterophyllum_ have not been found in connexion with fronds and their nature is problematical. This and other species are recorded by Krasser[1607] from the Lunz beds in Austria.

_Pterophyllum Bronni_ Schenk.

A Keuper species[1608] from Raibl in Carinthia distinguished by its large pinnae, 15 cm. or more in length and 0·5 cm. broad, and by their almost digitate disposition on the rachis. The fronds appear to be relatively short: the upper pinnae are highly inclined while the lower are given off at an obtuse angle; they are obcuneate or more or less oblanceolate, with a truncate asymmetrical apex and rounded angles; the base is slightly contracted. Arber[1609] has figured some specimens from the Munich Museum in one of which there are five spreading pinnae and a portion of the rachis; one pinna is undoubtedly attached and the others, though probably in place, are not in actual connexion with the axis. There is a close resemblance between this species and _Sphenozamites Rogersianus_ Font.[1610]: in the American type the fronds must have been 1 met. long; the leaflets, 19 × 9 cm., are elliptical, broadest near the apex and attached by the middle of the rounded base. Between the divergent and forked veins there is a fine granulation probably due to the presence of papillae. _Pterophyllum Bronni_ and _P. Rogersianum_ might be placed in Schimper’s genus _Macropterygium_[1611], though another Raibl species, originally described by Schenk as _Pterophyllum giganteum_[1612] and referred by Schimper to _Macropterygium_, has much longer and relatively narrow pinnae and agrees more closely with _Pterophyllum_ as the genus is usually defined. In order to emphasise the distinctive features of _Pterophyllum Bronni_ and Fontaine’s Virginian species they may conveniently be spoken of as _Pterophyllum (Macropterygium) Bronni_ and _Pterophyllum (Macropterygium) Rogersianum_.

_Pterophyllum Braunianum_ Goeppert.

In this Rhaetic species[1613] (fig. 613) the narrow linear pinnae, contiguous or more or less distant, are 1–2 mm. broad and may exceed 5 cm. in length though they are usually shorter; they are attached more or less at right-angles to the sides of a transversely wrinkled rachis. The base of the lamina is broadened and the veins are parallel, simple or forked. The epidermal cells have sinuous walls.

_Pterophyllum Tietzei_ Schenk.

A Rhaetic species founded[1614] on specimens from Persia and described also by Zeiller[1615] from Tonkin represented by fronds 1 met. long and at least 15 cm. broad. The segments, 3–7 cm. long and 8–18 mm. broad, are often set at right-angles to the rachis; the edges are parallel but the lower edge bends upwards at the apex. The veins are simple or forked and approximately 0·3 mm. apart.

_Pterophyllum Bavieri_ Zeiller.

This Rhaetic species from Tonkin[1616] and Persia[1617] is interesting as affording an example of a frond with exceptionally narrow and contiguous pinnae. The frond is narrow and lanceolate, 15–20 cm. long with pinnae normal to the rachis, ·5–1 mm. broad and 7–25 mm. long attached by the whole base which is sometimes slightly enlarged. The veins are simple or forked, ·15–·25 mm. apart: the apices of the segments are rounded or truncate and the form of the whole is similar to that of _Pterophyllum aequale_ but narrower.

_Pterophyllum_ (_Anomozamites_) _inconstans_ Braun.

In habit this Rhaetic species[1618] resembles _Nilssonia compta_. The linear-lanceolate fronds, as described by Zeiller[1619] in his Tonkin memoir, attain a length of 20 cm. and a breadth of 4 cm. The rachis, characterised by numerous transverse ridges, bears alternate or sub-opposite leaflets often at right-angles; they are almost rectangular and hardly longer than broad, attached by the whole of the base, which may be broadened, to the upper face of the rachis, but the lamina does not cover the whole of the rachis as in _Nilssonia_. The pinnae vary in breadth on the same frond and occasionally the lamina is continuous as in some forms of _Nilssonia_. Schenk[1620] figures examples from the Rhaetic of Franconia in which the lamina is very irregularly dissected and may be entire for a considerable distance. The epidermal cells have slightly sinuous walls. A similar type is represented by _Pterophyllum_ (_Anomozamites_) _Schenki_ Zeill.[1621], but the segments are contracted basally and become wider towards the apex where, as in _P. inconstans_, the edges are parallel. Feistmantel’s species _Platypterygium_ _Balli_[1622], though superficially similar to _Pterophyllum_, appears to agree more closely with _Pseudoctenis_.

_Pterophyllum Nathorsti_ Seward.

This species, founded on a specimen in the Sedgwick Museum, Cambridge, from the Middle Jurassic beds of Yorkshire, was formerly referred to the genus _Dioonites_[1623], but since the Yorkshire specimens were supplemented by material from Kimmeridge strata in Scotland[1624] affording more definite information with regard to the attachment of the pinnae it has been transferred to _Pterophyllum_. Pinnae laterally attached to the rachis which in some specimens shows a transverse wrinkling, narrow, linear, 3–4 mm. wide and reaching a length of 9 cm. The base of the segments is slightly expanded; the apex is acuminate or bluntly pointed: there are approximately three veins in 1 mm. of lamina. This type (fig. 614, A, B) is similar to _Pterophyllum aequale_ Brongn. as figured by Zeiller[1625] from the Rhaetic of Tonkin and agrees closely with some of the large Rhaetic specimens referred by Schenk to _P. Braunianum_. The Jurassic fronds from Oregon described by Fontaine[1626] as _Ctenophyllum angustifolium_ are similar forms and a specimen from the Wealden of Germany included by Schenk in _P. Dunkerianum_[1627] should probably be included in this species. Other closely allied forms are represented by _P. distans_ Old. and Morr.[1628] and _P. Footeanum_ from India.

_Pterophyllum_ (_Anomozamites_) _Nilssoni_ (Phillips).

The type-specimen, from the Jurassic beds on the Yorkshire coast and now in the York Museum, was described by Phillips[1629] as _Aspleniopteris Nilssoni_ and placed in _Pterophyllum_ by Lindley and Hutton and many other authors[1630]. The fronds are linear; the lamina may be almost entire or divided into unequal deep truncate segments; the veins are simple or dichotomously branched (fig. 615). The leaves are very similar to those of _Nilssonia_; they were probably borne on stems similar to those described by Nathorst as _Wielandiella_. Reference is made to the structure of the epidermal cells in the account of the genus.

_Pterophyllum_ (_Anomozamites_) _Lyellianum_ (Dunker).

This Wealden species, originally referred by Dunker[1631] to _Pterophyllum_, was afterwards transferred to _Anomozamites_[1632]. The fronds, in habit resembling the larger Rhaetic species _P. Braunianum_ Goepp., are characterised by the narrow linear pinnae of almost equal breadth attached approximately at right angles; there is a narrow line of rachis separating the two rows of segments (fig. 616).

{=CYCADITES.= Sternberg. {=PSEUDOCYCAS.= Nathorst.

The generic name _Cycadites_ was first used by Sternberg[1633] though it has since been shown that the specimens for which he proposed it belong to other genera. As employed by Brongniart[1634] and other authors _Cycadites_ stands for fossil fronds agreeing in habit with the pinnate leaves of recent species of _Cycas_ (fig. 387, A); the presence of a single median in the linear pinnae is generally regarded as an essential feature. _Cycadites_ may be defined as follows: Fronds pinnate; pinnae alternate or opposite, linear entire, with a midrib and no lateral veins, attached to the rachis by the entire base, the lower margin of which may be slightly decurrent or narrowed near the point of attachment. Epidermal cells with straight walls and stomata agreeing in structure with those of the recent genus. As thus defined, including the characters of the epidermal cells, the genus has no representatives; but the generic name should also be applied, as Miss Holden[1635] has recently suggested, to fronds of the _Cycas_ form which afford no information with regard to the structure of the epidermis. The resemblance of _Cycadites_ fronds to those of _Cycas_, coupled with the fact that impressions superficially resembling megasporophylls of the recent genus are recorded from Mesozoic strata, was considered sufficient justification for the employment of a name implying close affinity to or even generic identity with _Cycas_. A fuller knowledge of the epidermal characters of some of the fronds hitherto included in _Cycadites_ has necessitated the substitution of a new genus for _Cycadites_. An examination by Nathorst[1636] of Heer’s Lower Cretaceous Greenland species _Cycadites Steenstrupi_ and of other fronds showed that the epidermal cell-walls are sinuous and the stomata arranged differently from those of _Cycas_. For these and other reasons Nathorst proposed a new name _Pseudocycas_. He also pointed out that the pinnae in the fossil fronds have as a rule a double ‘midrib.’ Nathorst’s discovery raised the question whether other fronds described as _Cycadites_ should be transferred to _Pseudocycas_. Miss Holden’s investigation of other supposed Mesozoic representatives of _Cycas_ leads to the conclusion that ‘it is not impossible that all Mesozoic specimens of _Cycadites_ will turn out to be _Pseudocycas_.’ This observer shows that _Cycadites Saportae_ Sew. and _C. Roemeri_ Schk. agree in the sinuous walls of the epidermal cells with _Pseudocycas_; and so far no species of _Cycadites_, in which it was possible to examine the cuticular membrane, has been found that does not conform to Nathorst’s definition of _Pseudocycas_ at least as regards the structure of the epidermal cells. Nathorst defined _Pseudocycas_ in the following sense: Fronds similar to those of _Cycadites_ and _Cycas_ but with pinnae characterised by a double ‘midrib,’ the stomata being confined or almost confined to the groove between the two ‘midribs.’ Nathorst also notes that in _Pseudocycas_ the bases of the pinnae are not contracted as is often the case in _Cycadites_ and _Cycas_, but this is a feature of secondary importance. Miss Holden has, however, expressed the opinion that the double ‘midrib’ is an untrustworthy character and that the stomata are not always arranged as in the fronds examined by Nathorst. Nathorst states that in _Pseudocycas Steenstrupi_ and _P. insignis_ the midrib though usually double may be single: the same variation occurs in _P. Saportae_. Miss Holden found that an impression made from a pinna of _Cycas siamensis_ showed a double line on the upper face and a single rib on the lower; that is _Pseudocycas_ and _Cycas_ characters occur on a single pinna. On drying, the ridge on the lower face of the lamina collapses and a groove is formed bounded by two ridges.

In a recently published and interesting paper on ‘Some Xerophytic Leaf-structures in Mesozoic Plants,’ Dr Halle[1637] makes some important additions to our knowledge of _Pseudocycas_. He agrees with Miss Holden’s views with regard to the use of the generic names _Pseudocycas_ and _Cycadites_, but dissents from her interpretation of the median groove as the result of shrinkage of a midrib. Part of the evidence presented by Halle is based on the structure of the leaf-cuticle as shown in microtome sections[1638]. He found that a distinct median groove is always present on the pinnae of _Pseudocycas insignis_ and other species. If the groove were due to collapse of the tissue of a true median rib the presence of stomata—which in _P. insignis_ are confined to the middle line of the lamina—below the vein would be an unusual feature. He found no indication of a median vein or of any vascular tissue. All that is revealed by an examination of the cuticle is that the lamina has a well-defined groove bounded by prominent ridges, and in _Pseudocycas Roemeri_ the groove is deeper and is formed by the bending-back of the lamina. The stomata are practically confined to the groove and in _P. insignis_ and _P. Steenstrupi_ an additional protection against excessive transpiration was afforded by elongated papillae.

In the sinuous walls of the epidermal cells and in the structure of the stomata _Pseudocycas_ agrees with the Bennettitalean type as defined by Thomas and Bancroft[1639]. The ‘midrib’ of the pinnae marks the position of a pronounced groove and we have no information with regard to the venation. As Halle says, protection against drought is afforded by ‘other means than those usual among existing Cycads,’ which provide against excessive transpiration by the sinking of the individual stomata below the surface. The epidermal features of _Pseudocycas_ afford a striking example of the danger of basing conclusions on mere impressions and they further emphasise the great difference between Mesozoic Cycadean fronds and those of recent genera.

We have no knowledge of the nature of the reproductive organs of the plants which bore _Pseudocycas_ fronds, but the agreement of the stomata and epidermal cells with those in some Bennettitalean types favours the inclusion of the genus in that class. It has previously been pointed out that the impression figured by Heer[1640] in close association with the Greenland specimens of _Pseudocycas Steenstrupi_ as a carpellary leaf of the _Cycas_ type is much too imperfect to be identified and has no claim, as an examination of the actual specimen in the Copenhagen Museum convinced me, to be compared with a megasporophyll of _Cycas_. This view is shared by Nathorst.

In some cases the name _Cycadites_ has been applied to fragments that might equally well belong to Conifers or other plants, and not infrequently a careful examination of fossils referred to _Cycadites_ shows that the pinnae afford no evidence of a true midrib. Casts of revolute pinnae like those of the recent species _Encephalartos Ghellinckii_ (fig. 382) would present an appearance closely resembling a strong midrib. Heer’s Siberian Jurassic species _Cycadites sibiricus_[1641] is probably a piece of a _Taeniopteris_ or _Nilssonia_ frond, and _C. gramineus_ Heer[1642] should be referred to _Taxites_. An examination of the Indian fronds described by Oldham and Morris and Feistmantel as species of _Cycadites_ leads me to discard all of them as trustworthy records of the genus: in _Cycadites confertus_[1643] and _C. Blandfordianus_[1644] there appear to be several veins in the pinnae and not a single midrib. _Cycadites constrictus_[1645] is almost certainly a Conifer as Nathorst has also suggested. No satisfactory example of _Cycadites_ has been described from Palaeozoic strata; Goeppert’s _Cycadites gyrosus_[1646] is founded on material too imperfect to determine, and an examination of his Culm species _C. taxodinus_ in the Breslau Museum led me to refer it to a Conifer. The specimens figured[1647] by Zeiller from Lower Gondwana rocks in India as _Cycadites_? sp. are portions of linear leaves or leaflets 5 mm. broad with a median rib but they can hardly be accepted as evidence of the presence of a Cycadean plant.

_Pseudocycas insignis_ Nathorst.

The fronds of this Cenomanian species from the West of Greenland reach a breadth of 16 cm.; the rachis, 1 cm. broad, has two parallel ridges on the upper surface and to these are attached at a wide angle the broad bases of narrow linear pinnae reaching a length of 9 cm. and a breadth of 2–3 mm. (fig. 617). The pinnae are thick and separate and each has a double ‘midrib’ consisting of two parallel lines (fig. 617, B) which are occasionally replaced by one. The so-called double ‘midrib’ represents the two prominent ridges bordering the groove. The stomata, confined to the median groove, are approximately circular and the short epidermal cells have sinuous walls[1648].

_Pseudocycas Steenstrupi_ (Heer).

Nathorst refers this species, described by Heer as _Cycadites_, from the Cenomanian of Greenland, to _Pseudocycas_ on the ground that the epidermal cells are like those of _P. Steenstrupi_ and the stomata are confined to a median groove. Heer figures an impression in close association with the frond of this species which he identifies, without any adequate reason, as a carpellary leaf like that of a _Cycas_.

_Pseudocycas Saportae_ (Seward).

It has recently been shown by Miss Holden that this Wealden English species[1649] has the epidermal characters of _Pseudocycas_. In external form it agrees closely with _Cycadites tenuisectus_ Sap.[1650] from Lower Cretaceous rocks in Portugal, but nothing is known of the epidermal features of the latter type. The rachis is broad and flattened and bears alternate or sub-opposite pinnae of uniform breadth attached at right-angles or obliquely to its upper surface (fig. 618). The pinnae are 6–7 cm. long and about 1 mm. broad; their bases are slightly expanded and the apices sharply pointed. Miss Holden[1651] finds that the median rib is sometimes double and that the middle region of the lamina is covered with stomata; the epidermal cells have sinuous walls and stomata occasionally occur on each side of the main median stomatal area. Dr. Halle[1652] of Stockholm, who has examined cuticular preparations made from English specimens, confirms Miss Holden’s observations as regards the stomata, but he shows that there is no evidence of the existence of a midrib in the strict sense, the appearance of a single or double median vein being due to the presence of a dorsal stomatiferous groove, the edges of which would produce an impression on the matrix of a double vein or, if the groove became narrower, the impression would suggest a single midrib.

_Pseudocycas Roemeri_ (Schenk).

This Wealden species recorded from North Germany[1653] and the Sussex coast[1654] has broader pinnae laterally attached to the rachis. Miss Holden describes the stomata as covering the whole lower surface of the pinnae except over the midrib. This description must be revised in the light of Halle’s results obtained from an examination of the cuticle of the type-specimen of the species in the Berlin Museum. He finds that the edges of the pinnae are strongly revolute and thus form a deep dorsal canal which is almost closed[1655], a form of lamina, as seen in section, very similar to that of an _Empetrum_ leaf. The stomata are confined to the groove. It may be that the specimen examined by Miss Holden is specifically distinct or, as Halle also suggests, the cuticle obtained from the English fossil may not represent the whole surface but only the walls of the canal with possibly a portion of the cuticle of the outer dorsal surface. This type of leaf described by Halle is similar to that of _P. insignis_ with the xerophilous character intensified.

_Cycadites Saladini_ Zeiller.

This species was founded by Zeiller[1656] on fronds from the Rhaetic of Tonkin reaching a length of 40 cm. and 2–8·5 cm. broad with a rachis 3–4 mm. wide bearing contiguous linear pinnae 1·5–4·5 cm. long and 1·5–3 mm. broad with a more or less contracted base and a rounded or obtusely pointed apex. The pinnae are attached almost at right-angles or at an angle of 60°–80°. There is a clearly defined midrib.

It is not improbable that were the structure of the epidermal cells known this species would be found to be another example of _Pseudocycas_.

_Cycadites rectangularis_ Brauns.

This species[1657], first recorded from Rhaetic strata in Germany, differs in the narrower and more acutely pointed pinnae from _C. Saladini_. Miss Holden describes the midrib as double, but until specimens are found which admit of an examination of the cuticles it is impossible to decide whether it should be transferred to _Pseudocycas_. The species is widely distributed in Rhaetic and Jurassic strata and specimens are recorded from the Lias of Lyme Regis on the south coast of England.

_Cycadites Renaulti_ Lignier.

This species, from the Middle Lias of Normandy[1658], is founded on fronds 2·2–2·6 cm. broad with a rachis 3 mm. in breadth bearing laterally-inserted pinnae almost at right-angles 11–12 mm. long and 1·25–1·50 mm. broad; it is very similar to _C. rectangularis_ which occurs in the same beds.

II. +Nilssoniales.+

=NILSSONIA.= Brongniart.

This genus[1659] was named after the Swedish naturalist Nilsson who had figured certain plants from the Lias of Höör referred by Fries to the Ferns: these were named by Brongniart _Nilssonia brevis_ and _N. elongata_ and classed with the Cycads. The type-specimens of the latter species are regarded by Nathorst as a form of _N. brevis_. The history of the genus is fully discussed in Nathorst’s able monograph[1660]. _Nilssonia_, founded on fronds which with one exception are known only as casts or impressions, may be thus defined: Fronds with circinate vernation, at least in the type-species _Nilssonia brevis_ (fig. 619, C, D), similar in shape to the leaves of _Scolopendrium vulgare_ and _Polypodium irioides_ and to such unusual forms of _Cycas_ fronds as those reproduced in figs. 384, 387, I[1661], in which the laminae of the pinnae are concrescent and form a continuous or deeply cut lamina. They may reach a length of 60 cm. and a breadth of 10 cm. and some specimens are known in which the leaf is less than 1 cm. in width. The lamina is occasionally entire, but in the great majority of cases it is more or less deeply cut into segments of unequal breadth varying considerably in size and shape even in the same species, usually deep and truncate and sometimes long and narrow (_e.g. N. pterophylloides_, fig. 619, B). An important distinguishing feature is the attachment of the lamina to the upper face of the rachis which it covers: the extension of the lamina over the surface of the frond axis and the rare occurrence of branching of the veins are characters in which _Nilssonia_ differs from _Taeniopteris_. The veins are given off at right-angles or obliquely from a very narrow groove occupying the median line of the rachis; they are nearly always simple and in some of the more fleshy leaves, _e.g. N. brevis_, they are seldom visible. The surface of the lamina may be smooth or transversely corrugated. The rachis forms a prominent rib on the under surface of the frond (fig. 620, A) and may be continued beyond the lamina as a short petiole. Epidermal cells polygonal or rectangular, with straight walls in contrast to the sinuous walls of _Taeniopteris_; some of the cells bear strongly cuticularised papillae, possibly the bases of hairs (compare the hairs on the fronds of _Acrostichum crinitum_, a Fern with leaves similar in shape to some of the large entire fronds of _N. orientalis_ though relatively broader and with anastomosing veins). Stomata usually confined to the lower epidermis and not very numerous; guard-cells of rounded contour and without any special thickening surrounded by 6–8 accessory cells with thickened walls (fig. 611, B) forming a chimney slightly raised over the stomatal pore[1662]. In _Nilssonia_ the guard-cells do not exhibit that regularity of orientation which characterises the stomata of _Ptilophyllum_, _Otozamites_, and other Bennettitalean fronds. Little is known of the anatomy of the leaves: in a petrified leaf of _N. orientalis_[1663] from Upper Cretaceous rocks in Japan there is no palisade-tissue and small groups of sclerenchyma occur above and below the veins. The xylem appears to be centripetal, but the preservation is far from satisfactory. A few secretory canals were found near the edge of the leaf. We have no certain knowledge of the reproductive organs. The small circular projections figured by Schenk[1664] on some leaves of _Nilssonia polymorpha_ as sporangia have no claim to be so regarded. In the description of _N. brevis_ reference is made to some seeds discovered by Nathorst which may belong to that species. Nathorst suggests the possibility that the Rhaetic fossil _Stenorrachis scanicus_ Nath. may be the seed-bearing shoot of a _Nilssonia_, either _N. brevis_ or _N. polymorpha_, and if this surmise is correct it almost necessarily involves the genus _Beania_[1665] which has been tentatively referred to the Ginkgoales though without any convincing evidence to support such connexion. Nothing is known of the stems: the occasional occurrence of leaves converging towards a common support points to a Cycadean habit. It is possible, as Nathorst suggests, that the Rhaetic species _Bucklandia Saportana_[1666] may be the stem of a _Nilssonia_.

_Nilssonia_ is especially characteristic of Jurassic and Rhaetic floras; it occurs also in Triassic beds and extends into Cretaceous floras.

Nathorst instituted the genus _Nilssoniopteris_[1667] for some specimens from the Yorkshire coast which he believed to be examples of _Nilssonia tenuinervis_ on the ground that the veins are dichotomously branched and the epidermal cells have sinuous walls. Mr Hamshaw Thomas[1668] has, however, shown by an examination of the specimens in the Stockholm Museum that they belong to _Taeniopteris vittata_, and Prof. Nathorst agrees with this conclusion. The name _Nilssoniopteris_ must therefore be abandoned. Miquel[1669] proposed the name _Hisingera_ for some _Nilssonia_ fronds, but it has not been adopted.

_Nilssonia polymorpha_ Schenk.

Linear fronds varying considerably in breadth and in the degree of dissection of the lamina, which may be entire; the margin may show broad and shallow crenulations or there may be a few narrow and deep sinuses cutting the otherwise entire lamina into long and narrow segments. More usually the lamina is divided to the rachis into numerous truncate segments traversed by parallel, simple, veins extending from a narrow groove in the middle of the rachis on the upper surface of the frond (fig. 619, E). The veins run in very narrow grooves in the generally flat but occasionally corrugated lamina[1670].

This species agrees very closely in habit with _N. compta_ and _N. brevis_ and, as Nathorst points out, it is in some cases almost impossible to distinguish _Nilssonia polymorpha_ from _N. brevis_. Some of the fronds from the Rhaetic of Franconia described by Schenk as _N. polymorpha_ are examples of _N. brevis_. In _N. polymorpha_ the distal ends of the segments are blunter, the lamina is much less folded and when folds or corrugations occur they are less regular than in _N. brevis_. The epidermal cells are polygonal and have thick, straight, walls: oval or circular papillae occur both on the lamina and rachis. The stomata, confined to the lower surface, are between the veins and each is accompanied by a ring of subsidiary cells (_cf._ fig. 611, B). _N. polymorpha_ is a member of Rhaetic floras and is recorded also from Liassic rocks at Höör[1671].

_Nilssonia brevis_ Brongniart.

This species[1672] (fig. 619, C, D), one of those from Höör on which the genus was founded, has been very fully investigated by Nathorst[1673] whose researches have cleared up many obscure features. The young fronds are circinate like those of Ferns and _Cycas_. The linear fronds agree generally in habit with those of _N. polymorpha_ and _N. compta_, but the lamina is thicker and is characterised by regular transverse corrugations; the veins are very rarely visible except in young leaves which have not reached their full thickness. The fronds may be 50 cm. long and vary in breadth from 1·5 to 12 cm.; the petiole is very short or the frond may be sessile. Between the regular grooves on the upper surface the lamina is more or less convex; seen from below the grooves are represented by ridges and between each pair of ridges there are parallel folds, sometimes three (fig. 620, B) or as many as six; and where the segments are narrow, that is the strips of lamina between two grooves (or ridges), there may be only a single fold which gives the appearance of linear segments with a single midrib as in _Cycadites_, a misleading resemblance of special interest in reference to the _Nilssonia_ fronds described by Oldham and Morris[1674] and by Feistmantel[1675] as _Cycadites rajmahalensis_. Owing to the fleshy nature of the leaf the difference between the upper and lower side is particularly well marked in this species. The lamina may be more or less entire, but is usually divided by deep sinuses extending to the rachis into truncate or distally tapered segments varying in breadth (fig. 619, C, D), the narrow segments being characterised by a more pointed apex than in _N. polymorpha_. The structure of the stomata and epidermal cells is of the type described in the definition of the genus. Strongly cuticularised papillae, incorrectly described by Schenk[1676] in _N. polymorpha_ as stomata, occur on some of the epidermal cells: these may be the bases of hairs. In some preparations Nathorst found patches of a resinous substance, an interesting discovery in view of the occurrence of secretory canals in the petrified leaf of _Nilssonia orientalis_ described by Dr Stopes[1677].

_Nilssonia brevis_ occurs in Upper Rhaetic and Lower Liassic strata.

_Nilssonia pterophylloides_ Nathorst.

A Rhaetic Scanian species originally referred by Nathorst[1678] to _Nilssonia_ but later removed by him to _Dioonites_[1679] and in 1909 reinstated in _Nilssonia_[1680] on the ground that the lamina covers the upper face of the rachis. The segments are fairly uniform in breadth and linear; they reach 10 cm. in length and are usually 5–7 mm. broad; the lamina is slightly tapered towards the apex (fig. 619, B). There are 3–10 parallel grooves on the upper face of the segments and between each pair is a single unbranched vein. In close association with portions of three fronds of this species Nathorst found several oval bodies, 1 cm. × 7 mm., which he at first regarded as ‘antherangia’ comparable with the sporocarps of the Hydropterideae, but an examination of the carbonised tissue demonstrated that the small rounded bodies contained in each of the ‘antherangia,’ originally believed to be pollen-sacs, are grains of resin internal to a cuticle of thick-walled cells and probably formed by secretory sacs in a fleshy tissue. Internal to the resin-bodies is a second cuticle which may be the remains of a nucellus, the outer cuticle and the resin belonging to the sarcotesta. Nathorst’s careful examination of these fossils shows that they are seeds (fig. 619, A) and were probably borne on plants of _N. pterophylloides_, though an accidental association is not improbable.

_Nilssonia compta_ (Phillips).

Broadly linear fronds varying considerably in size and in the breadth and number of the truncate segments. In some cases the fronds exceeded 40 cm. in length and had a breadth of 9 cm. (fig. 622). The veins are simple, parallel, and fairly prominent and the lamina shows clearly the attachment to the upper surface of the rachis which is covered by it as in all species of the genus[1681]. The structure of the epidermis and stomata has recently been described by Thomas[1682]. Brongniart mentioned in the _Prodrome_ a species from the Lower Oolite of Yorkshire under the name _Pterophyllum Williamsonis_[1683], but in a later work this is given as a synonym of _N. compta_. _Nilssonia compta_ bears a close resemblance in habit to _N. polymorpha_; it agrees also with the large fronds described from the Upper Gondwana of India as _Pterophyllum princeps_[1684]. Since attention was first called to this similarity an examination of several of the figured specimens has convinced me that the Indian fronds are either identical with or at least closely allied to the European leaves. The apparent lateral attachment of the lamina in the drawings published by Oldham and Morris and Feistmantel is due to imperfect preservation; the lamina ends in two raised ridges, and the discovery of a specimen in which the lamina completely covers the rachis confirmed the impression made by the other specimens. The Amurland Jurassic species _Nilssonia Schmidtii_[1685] Heer though probably not identical with _N. compta_ is a very similar type; it was originally described by Heer as _Anomozamites Schmidtii_ and transferred by Nathorst[1686] to _Nilssonia_: the veins are occasionally forked near the rachis and are rather farther apart (·5 mm.) than in _N. compta_ and the segments are broader and deeper than in the English species. _Nilssonia nipponensis_ Yok.[1687] a Jurassic species recorded from Japan and North America is another similar type.

_Nilssonia orientalis_ Heer.

In this Jurassic and Lower Cretaceous species, founded on material from Jurassic rocks in Siberia[1688], the lamina is generally entire. The fronds exhibit a wide range in size and shape; they may have the form of very narrow linear leaves barely 1 cm. across or may reach a breadth of nearly 10 cm. The leaves from Middle Jurassic British strata named by Nathorst _N. tenuinervis_[1689] are probably identical with Heer’s type, and _N. Johnstrupi_[1690] Heer from the Lower Cretaceous of Greenland may also be referred to _N. orientalis_.

The veins are at right-angles or oblique to the rachis and are very numerous, three or more in a breadth of 1 mm.[1691] A species recently described by Halle[1692] from Graham Land as _N. taeniopteroides_ agrees closely in habit with _N. orientalis_: in the southern form the frond may have a length of 40–50 cm. and a breadth of 3 cm. The entire lamina of _N. taeniopteroides_ tapers gradually towards the base and is more rapidly narrowed in the distal region; the petiole is at least 6–7 cm. long: the simple or branched veins, 15–20 in 1 cm., are given off from the axis at a wide angle. The more crowded veins in _N. orientalis_ constitute one of the few features in which it differs from Halle’s species, but the fact that the degree of closeness of the veins is inconstant within the same species renders this distinction of doubtful value. Halle compares his species also with _N. densinervis_ (Font.) originally described as _Platypterigium densinerve_ from the Potomac beds[1693] and afterwards transferred by Berry[1694] to _Nilssonia_ and considered by him to be identical with Fontaine’s _Platypterigium Rogersianum_. An examination of some of Fontaine’s specimens in the Washington Museum led me to refer the fronds to _Nilssonia_[1695].

It is impossible to speak with confidence as to the absolute specific identity of _N. orientalis_ Heer, _N. Johnstrupi_ Heer, _N. taeniopteroides_ Halle, and some similar forms; but it is clear that the linear fronds of this type characterised by an entire or occasionally pinnatisect lamina were widely distributed in Jurassic and Lower Cretaceous strata and persisted to the Upper Cretaceous series in Japan. This form of frond is recorded from England, Scotland, North America, Greenland, Spitzbergen[1696], Siberia, Russia, Afghanistan[1697], Japan[1698], Graham Land, and elsewhere. Reference has already been made to a petrified specimen of _N. orientalis_ described by Dr Stopes from Japan[1699].

Specimens described by Salfeld[1700] from the Corallian of Germany as _Taeniopteris_ sp. may be _N. orientalis_; Bartholin’s _N. polymorpha_ from Bornholm, Velenovský’s Lower Cretaceous _N. bohemica_ and Yokoyama’s _N. ozvana_ from Japan are other examples of fronds which may be identical with _N. orientalis_[1701].

_Nilssonia tenuicaulis_ (Phillips).

This Jurassic species, while agreeing generally in habit with _N. compta_, is characterised by the narrow and numerous linear segments with a more acuminate apex. The fronds reached a length of more than 20 cm.[1702] Leckenby’s name _Pterophyllum medianum_[1703] was given to a specimen from the Yorkshire coast and now in the Sedgwick Museum, Cambridge, which, with _Pterophyllum angustifolium_, is clearly identical with _Cycadites tenuicaulis_ Phillips. The specific name _mediana_ frequently used[1704] for this type should be given up in favour of the older term _tenuicaulis_. A species of similar habit is described but not figured by Krasser[1705] as _N. Sturii_ from the Lunz beds. _N. tenuicaulis_ is fairly common in the Middle Jurassic beds near Scarborough and is recorded from the Kimmeridgian of Scotland under the name _N. mediana_ (fig. 614, C)[1706].

_Nilssonia princeps_ (Oldham and Morris).

Oldham and Morris speak of _Pterophyllum princeps_[1707] as one of the commonest plants in the Rajmahal beds in India. The fronds are characterised by their large size and by the very broad oblong and distally truncate pinnae with parallel and occasionally branched veins. In the specimens figured by Oldham and Morris and Feistmantel the pinnae are cut off at their bases (fig. 623), which form ridges parallel to the rachis: this feature is not clearly shown in the published drawings. By breaking some pieces of rock from a slab containing figured specimens other pieces were found in which the laminae of the bases of segments meet in the middle of the upper face of the rachis. The pinnae vary in breadth from 1 cm. to 3·5 cm. and reach a length of 8 cm.; the distal end is truncate, the lower edge being strongly curved: the segments are slightly broadened at the base. The veins are prominent and parallel, from 0·5 to 0·8 mm. apart. The Rajmahal fronds described as _Pterophyllum Morrisianum_[1708] appear to be indistinguishable from this species.

_Nilssonia Schaumburgensis_ (Dunker).

This species, first described as _Pterophyllum Schaumburgense_[1709] from the Wealden of Germany, affords a good illustration of a small type of frond closely resembling the much larger species _N. compta_. Examples from English Wealden rocks seldom exceed 1 cm. in breadth and are often much narrower; the linear lamina is almost entire or divided into short and broad truncate segments of unequal breadth: the veins are parallel and simple. For figures of this species, recorded from different European localities and from Japan, reference should be made to the accounts by Schenk[1710], Nathorst, Yokoyama, Yabe, and Fontaine.

=CTENIS.= Lindley and Hutton.

The genus _Ctenis_[1711] was founded on a piece of pinnate frond from the Middle Jurassic rocks of the Yorkshire coast previously figured by Phillips as _Cycadites sulcicaulis_. Lindley and Hutton regarded the plant as probably Cycadean and proposed to apply the name _Ctenis_ to all leaves having the general characters of Cycadeae, but with ‘the veins connected by forks or transverse bars.’ While many authors have accepted _Ctenis_ as a Cycadean genus, by others[1712] it has been placed among the Ferns, on the ground that some small circular elevations on the lamina of the segments of certain species are believed to be sori or sporangia. Since Ettingshausen[1713] and Schenk[1714] first noticed this feature Raciborski[1715] has figured several examples from Poland and Staub[1716] records similar circular bodies on a Liassic Hungarian species. In no single instance have sporangia been found. Nathorst[1717] proposed the designation _Anthrophyopsis_ (because of the resemblance of the lamina in form and venation to the leaves of the Fern _Anthrophyum_) for some Rhaetic specimens from Scania, but as they were subsequently found to be segments of a pinnate frond he adopted the name _Ctenis_. An example in the Manchester Museum[1718] (fig. 624) from Yorkshire, mentioned by Nathorst in an early paper as probably a new species of _Anthrophyopsis_, afforded good preparations of the cuticle (fig. 625) which revealed the existence of circular elevations on the outer walls of the epidermal cells: these may explain the nature of some at least of the supposed sporangia. The walls of the epidermal cells are straight. The name _Ctenis_ is applied to pinnate fronds which are probably Cycadean though we have no evidence as to the nature of the stem or the reproductive organs. _Ctenis_ fronds are among the largest Cycadean leaves from Mesozoic floras; in _Ctenis hungarica_ Staub the frond is said to have reached a length of 2 met. and in other species the dimensions exceed those of most pinnate leaves. The stout rachis bears linear or broad-oblong pinnae attached at a wide angle and varying considerably in size and shape; the pinnae are attached by the whole base which is usually broadened and decurrent but in a few cases slightly contracted (_e.g._ _C. Zeyschneri_ Rac.[1719]). For some fronds bearing broad and basally narrowed segments Raciborski proposed the name _Ctenidiopsis_ in distinction from _Euctenis_ which he applies to the typical forms. The pinnae may be long and narrow reaching a length of over 12 cm., or short and broad: in some cases the frond would be more correctly described as deeply pinnatisect; the apex of the segments is acute, bluntly rounded or truncate. Several veins pass into the base of each pinna and pursue a course approximately parallel to the edge of the lamina; a characteristic feature is the occasional occurrence of oblique cross-connexions between the veins. It is possible that in some species the pinnae had spinous margins as in the pinnae of uncertain affinity figured by Fontaine[1720] as _Encephalartopsis nervosa_ from the Potomac series. Our knowledge of the epidermal cells is very meagre: in the specimen represented in fig. 625 the epidermal cells have straight walls and a central papilla. The genus extends from Triassic to Upper Jurassic rocks.

_Ctenis lunzensis_ Stur.

This species, first recorded by Stur from the Lunz Upper Triassic flora, has recently been examined by Krasser[1721] and compared with the Jurassic species _Ctenis sulcicaulis_ (Phill.) (= _C. falcata_ Lind. and Hutt.) and _C. Potocki_ Rac. No figures or detailed descriptions have been published.

_Ctenis fallax_ Nathorst.

This Scanian Rhaetic type[1722], including _Anthrophyopsis crassinervis_, _A. Nilssoni_, and probably _A. obovata_ Nath., is characterised by very large obtusely pointed pinnae reaching at least 20 cm. in length and over 3 cm. in breadth. The veins are often 2 mm. apart and form long polygonal meshes. Nathorst figures small circular patches on the surface of the lamina. Raciborski[1723], on slender evidence, refers a fragment from the Jurassic of Cracow to this species.

_Ctenis hungarica_ Staub.