552 PTERIDOSPERMS, ETC. [CH. 



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 r^sum^ of opinions 

 expressed by other authors in regard to the position of Pachy- 

 pteris (= Dichopteris) and decides in favour of a Cycadean 

 alliance. 



A French Jurassic plant which Saporta^ 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 reason- 

 able 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 Palae- 

 ozoic 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^ instituted the genus Odontopteris for compound 

 fronds from the Coal-Measures characterised by pinnules at- 

 tached 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^" 



' Saporta (73) A. PI. xlvii. = Brongniart (28) A. p. 60. 



3 Kidston (Ol^) p. 196. 



