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.
Fig. 363. Dichopteris visianica, Zigno. (⅓ nat. size. After Zigno.)