Ctenis sp.
The pinna shown in fig. 624 from the Jurassic beds in Yorkshire[1737] is interesting as one of the few examples of the preservation of the cuticular membrane. The straight or curved walls of the epidermal cells agree with those of recent Cycads except Stangeria, and each cell bears a large central papilla that gives to the lamina the finely punctate appearance which has been regarded as evidence of sporangia. The gaps in the cuticle probably mark the position of sunken stomata.
PSEUDOCTENIS. Seward.
This genus[1738] was established for certain pinnate fronds agreeing in habit with Ctenis sulcicaulis but distinguished by the almost complete absence of any cross-connexions between the veins. Some of the forms with narrow pinnae closely resemble species of Zamites, the distinguishing feature being the decurrent lower margin of the leaflets. Though such fronds might not unreasonably be included in Ctenis, it is more convenient on the analogy of the occasional occurrence of Glossopteris fronds with very few anastomoses to employ a distinctive designation.
Pseudoctenis eathiensis (Richards).
Some of the specimens on which this species[1739] is founded were originally figured by Miller[1740] from Upper Jurassic strata in Scotland and afterwards named by Richards[1741] Zamites eathiensis. The general appearance of the fronds is very like that of Ctenis sulcicaulis; the pinnae vary in breadth from about 3 mm. to 1·5 cm.; they are attached at right-angles or, in the apical region, may be almost parallel to the rachis. The longest pinna recorded is 17 cm. and the lamina tapers to a slender apex; the veins are parallel and occasionally forked, but cross-connexions are rare. The partially petrified rachis of one specimen showed hypodermal stereome and some secretory canals as in recent Cycads. The specimen from Wealden rocks near Hastings (fig. 627), originally described as Zamites sp.[1742], is probably specifically identical with Pseudoctenis eathiensis. The South African Wealden species, originally described by Tate as Palaeozamia Rubidgei[1743], agrees closely with Pseudoctenis and is probably an example of that genus. This type bears a close resemblance in the form of the frond to Ctenophyllum grandifolium Font.[1744] and C. Wardi[1745] Font. from American Trias and Jurassic rocks respectively. Pseudoctenis crassinervis Sew.[1746] is another Scotch form with coarser veins.
A frond very similar in habit to P. eathiensis is represented by Pseudoctenis ensiformis Halle[1747] from the Jurassic strata of Graham Land originally referred by Nathorst to Pterophyllum. An examination of the type-specimen in the Stockholm Museum revealed its resemblance to the Scotch species P. eathiensis: a single anastomosis was noticed in one of the pinnae. The broadly ensiform obtuse pinnae, reaching a length of 7 cm. with a maximum breadth of 3 cm. at their expanded bases, vary in breadth and are attached at right-angles to a slender rachis. The veins, 1–1·5 mm. apart, are parallel and strong. The varying breadth of the pinnae irrespective of their position on the rachis is a distinctive feature. Halle draws attention to a resemblance of this Antarctic species to Ctenophyllum latifolium Font. a Potomac type referred by Berry[1748] to the genus Ctenopsis on the rather slender ground that the veins are arranged in pairs. Berry in a footnote expresses the opinion that Ctenopsis is very closely related to or possibly identical with Pseudoctenis.
If the bases of the pinnae in the specimen of P. ensiformis figured by Halle are complete, as they appear to be, the frond agrees very closely with Pterophyllum Carterianum Old. and Morr.[1749] from India. A comparison of the Rajmahal specimen with Halle’s figure leads me to regard the two fronds as probably identical. The veins in the Indian species, which should also be referred to Pseudoctenis, are prominent and from ·5 to 1 mm. apart; the base of the lamina is slightly broadened and the veins curve downwards towards the rachis in the lower decurrent portion. The other Indian type, Pterophyllum Morrisianum[1750], with which Halle compares his species is, however, not a Pseudoctenis but should be included in Nilssonia and is probably identical with Pterophyllum princeps Old. and Morr.
Pseudoctenis Lanei Thomas.
This species[1751], recently described from Middle Jurassic beds at Marske, Yorkshire, has narrower linear lanceolate pinnae. The linear pinnae reach a length of 10 cm. and a breadth of 9 mm. The veins are numerous, 10 in a breadth of 6 mm., and only one cross-vein was noticed. In the decurrent lower edge of the laminae the fronds are identical with Ctenis sulcicaulis. A very good example of this species[1752] in the York Museum is reproduced by Mr Thomas in his account of Cleveland Jurassic plants.
Pseudoctenis Balli (Feistmantel).
A species described originally by Feistmantel[1753] as Anomozamites Balli from the Barakar group of the Damuda series and afterwards transferred to the genus Platypterygium, characterised by broadly linear segments of unequal breadth attached obliquely or at right-angles to a slender rachis. The apices of the segments though usually imperfect appear to be truncate; the bases of the pinnae are decurrent by their lower edge. The veins are approximately 3 per millimetre; they are generally forked at the base and in one or two places show cross-connexions. In the middle of the frond the narrow rachis is exposed but in the apical region it is covered by the laminae. The occurrence of two divergent pinnae at the apex of the frond is a feature met with also in Ctenis sulcicaulis. This description is based on an examination of the specimens figured by Feistmantel.
III. Cycadean Fronds which cannot be assigned to a family-position.
SPHENOZAMITES. Brongniart.
This name was proposed by Brongniart[1754] as a subgenus of Otozamites denoting pinnate fronds bearing leaflets without an auriculate base: he suggested that the subgenus might eventually be raised to generic rank and this was done by Zigno[1755] though in too wide a sense. In the case of Otozamites Beani (Lind. and Hutt.), quoted by Brongniart in illustration of Sphenozamites, the latter designation is inapplicable as the pinnae are auriculate. Another species, Zamites undulatus Sternb., to which Brongniart applied his new subgeneric term, is probably identical with Otozamites acuminatus (L. and H.)[1756].
Although the distinction between Sphenozamites and Otozamites is often ill defined the former name may be conveniently adopted for pinnate fronds similar to those of Zamia Skinneri and some species of Encephalartos characterised by leaflets of an asymmetrical, obovate, or rhomboidal form with a contracted or cuneate base and numerous branched divergent veins. Nothing is known of the structure or reproductive organs of Sphenozamites, and the genus, though serving a useful descriptive purpose, is founded solely on form, and in the absence of other data it would be rash to assume that its use implies close natural affinity. In the case of many other genera of Cycadean fronds there is additional evidence of relationship, but this is not the case with Sphenozamites. The pinnae resemble those of such recent Cycadean fronds as Zamia Skinneri and Z. muricata. The genus ranges from Lower Permian to Jurassic rocks.
Sphenozamites Rochei Renault.
This species[1757], from the Lower Permian of the Autun district, is founded on a pinnate frond bearing alternate pinnae, 2·5 × 1 cm., with an asymmetrical oblong lamina attached obliquely near the edge of the rachis with a cuneate base slightly decurrent below and a broadly rounded apex; the veins dichotomise once or twice as they diverge from the narrow base (fig. 628). The pinnae resemble the leaflets of Noeggerathia foliosa Sternb. and are similar in shape to those of the Jurassic species Sphenozamites Geylerianus Zig.
Sphenozamites Belli Seward.
This Middle Jurassic species from Stonesfield[1758] is founded on detached pinnae possibly identical with a specimen figured by Buckman as ?Naiadea obtusa[1759]. The pinnae are wedge-shaped, tapering gradually to an acute apex and attached by a narrow base: the leaflet shown in fig. 629 is 9 cm. long; the veins are numerous and more divergent than in some leaves of similar form referred to the genus Podozamites. With this species may be compared several Italian Jurassic specimens described by Zigno[1760] as four distinct species but more appropriately assigned to a single type S. Geylerianus. An examination of Zigno’s fronds in the Padua Museum, which he named S. Rossii, leads me to regard the irregularly serrate edge of the pinnae as the result of tearing of an originally entire lamina and to compare the specimens with Otozamites Beani (L. and H.). An imperfect ovoid pinna recalling S. Belli is figured by Newberry from the Rhaetic of Honduras as Sphenozamites robustus[1761]. A French Upper Jurassic species figured by Saporta as Sphenozamites latifolius bears a very close resemblance in the form of the leaflets to the Wealden plant Sewardia latifolia[1762]. Kurtz records the occurrence of Sphenozamites, S. Geinitzianus, from Rhaetic strata in Argentina[1763], but I have not seen any figures of this species.
PLAGIOZAMITES. Zeiller.
The name Plagiozamites was proposed by Zeiller[1764] for some pinnate fronds and detached leaflets from the Stephanian of Commentry and the Lower Permian of the Vosges. The better preservation of the Vosges material enabled him to recognise certain features which led to the substitution of Plagiozamites for Zamites, the name originally employed by Renault for the Commentry specimens. Plagiozamites bears a superficial resemblance to Zamites and Otozamites and differs but little from Sphenozamites and Noeggerathia; it stands for pinnate fronds bearing ovate pinnae with a sub-amplexicaul oblique attachment to the rachis as is clearly shown in the species P. Planchardi (Ren.)[1765]. In the case of Palaeozoic fronds assigned to the Cycadophyta on the ground of the resemblance of their pinnae to those of undoubted Cycadean species, it is particularly important to recognise the fact that decisive evidence as to systematic position is lacking. We know nothing of the stem, the reproductive organs, or the epidermal and stomatal characters of Plagiozamites, and it is by no means certain that the genus is a true representative of the group in which it is provisionally included.
Plagiozamites Planchardi (Renault).
Fronds pinnate; pinnae ovate-lanceolate reaching 5 cm. in length and 1·6 cm. in breadth, inserted obliquely on the rachis, but not along a line parallel to the long axis of the rachis as in Zamites, and partially embracing it: the edge of the lamina is finely denticulate; veins slightly divergent and occasionally branched. The leaflets are narrow and more acute than those of Noeggerathia and Sphenozamites Rochei Ren. Plagiozamites is recorded from the Stephanian of Commentry, the Coal Measures of Manchuria[1766], and the Lower Permian of the Vosges. Renault described six species of Zamites from Commentry all, except Z. carbonarius, based on detached pinnae. The type-specimen of Z. carbonarius consists of a piece of stout rachis bearing ovate acute pinnae, 2·2 × 1 cm. Potonié[1767], who refers a piece of pinnate frond from the Permian of Thuringia to Z. carbonarius, includes the other species of Renault under that name. Whether or not the differences in the venation and form of the pinnae are of specific significance cannot be definitely settled without better material, but the important point is that these Permo-Carboniferous fronds are sufficiently distinct from Zamites to be placed in a separate genus. Plagiozamites carbonarius is recorded also by Zalessky[1768] from the Permian of Manchuria though the examples figured do not afford satisfactory evidence of the mode of insertion of the segments on the rachis. P. Planchardi has recently been recorded from the Coal Measures of Maryland; the discovery is interesting both on phytogeographical grounds and as the first satisfactory record of a Palaeozoic Cycadophyte from North America[1769].
Cycadorachis. Saporta.
The employment of this generic name may serve a useful purpose if used for specimens, whether preserved as petrifactions or impressions, believed to be portions of Cycadean frond-axes, but which in the absence of pinnae cannot be assigned to one of the recognised genera of fronds. Saporta[1770] describes two species from Kimmeridgian beds in France, Cycadorachis abscissa and C. armata: the first may be the winged base of a Cycadean petiole, but it agrees equally well with the broad base of an Osmundaceous leaf and should not be referred to a genus implying affinity with a particular class. The other species, C. armata, is probably a piece of a spinous axis like that of the Wealden plant Sewardia latifolia (Sap.). A fragment figured by Fliche and Bleicher[1771] from the Jurassic of Nancy as C. tuberculata is another example of a fossil which cannot be referred with any certainty to the Cycads.
Dr Stopes[1772], inadvertently overlooking the previous institution of Cycadorachis, has recently proposed the name Cycadeorachis for pinnately branched rachises of Cycadean fronds which, ‘while indicating the general character of the frond, do not show the shape of the pinnae well enough to be associated with any of the many foliage-genera.’