678 PROFESSOR A. C. SEWARD ON 



Thinnfeldia de Geeri (Nathorst). (PI. V. fig. 80.) 



1897. ? Sphenopteris de Geeri, Nathorst, Kongl. Svensk. Vet. Akad. Hand., Bd. xxx., No. 1, p. 48, 



pi. ii. fig. 8, pi. vi. fig. 1. 



The imperfect leaflet represented in fig. 80, though too small to determine with 

 confidence, bears so close a resemblance to the specimens described by Nathorst from 

 the Upper Jurassic of Spitzbergen that I venture to adopt his name, with the substitu- 

 tion of Thinnfeldia for Sphenopteris. A similar type is figured by Kerner from the 

 Lower Cretaceous of Lesina as Pachypteris dimorpha* 



Thinnfeldia sp. (Photo. 14, PI. VII.) 



The branched axis represented in PI. VII. fig. 14 probably belongs to a Thinnfeldia 

 frond ; it shows the characteristic V-shaped form of branching which is a feature of 

 the genus. 



Dichopteris, Zigno. 



Dichopteris Pomelii (Saporta). (PI. III. figs. 55, 55 A ; PL IV. fig. 71.) 



1873. Scleropteris Pomelii, Saporta, Pal. Frang. Jurass. Flor., i. p. 370, pis. xlvi., xlvii. 



The fragment shown in fig. 71, PI. IV., considered by itself might well be regarded 

 as specifically identical with fig. 82, PL V. (T. rhomboidalis), but in another specimen 

 pinnules of the same size are borne on short pinnae attached at an acute angle to a 

 piece of rachis. More important evidence is afforded by the specimen shown in fig. 55, 

 PL III., in which we have a strong rachis bearing portions of pinnae with bluntly 

 terminated pinnules like those in fig. 71. No veins are visible. The genus Scleropteris 

 was founded by Saporta on French Jurassic specimens characterised by a rigid 

 coriaceous habit, bearing pinnules more or less contracted at the base and usually 

 showing no venation. Under this name he included some species previously referred 

 to Dichopteris and Pachypteris, but, as I have elsewhere t stated, the reasons for the 

 creation of an additional genus do not appear to be adequate. There can be little 

 doubt that fronds described by authors under Dichopteris are very closely related to 

 Thinnfeldia, but Zigno's genus may be conveniently retained for such smaller forms as 

 Scleropteris Pomelii Sap. The specimen shown in fig. 55, though imperfectly pre- 

 served, agrees so closely with Saporta's species from the Corallian of France, that I 

 have adopted his specific designation. 



? Dichopteris sp. (Text-fig. 8, A, B.) 



The fragment represented in fig. 8, A, may be specifically identical with D. Pomelii, 

 but, on the other hand, it may belong to a small pinna of a Thinnfeldia frond. The 

 venation is clearly shown ; a few secondary veins arise at an acute angle from a 

 slender midrib. 



* Kehner (95), pi. iii. t Seward (10), p. 552. 



