GENERAL OBSERVATIONS ON THE FLORA. 95 



Danseopsis than any other, yet the points of difference are very significant. 

 Pseudodanseopsis is clearly, in its reticulated nervation, a higher type than 

 Danseopsis, and this points to a later age for it. 



The genus Ctenophyllum is characteristic of the Rhsetic and Jurassic 

 formations. The species C. grandifolium finds its analogues in the large 

 Pterophylla of the Jurassic formation of India, of the type of P. Footeanum. 

 The genus Podozamites is Rhsetic and Jurassic. Podozamites tenuistriatus is 

 more like P. angustifolius Schenk, of the Rhsetic of Europe, than any other 

 plant, while P. JEmmonsi finds its nearest relatives among Oolitic forms. 

 Sphenozamites Bogersianus is evidently one of the most complex of the 

 species of this genus, which Saporta considers to be the highest in grade 

 among the Cycadaceous plants. Sphenozamites is a Jurassic type. We 

 find, then, that the generic character of the species peculiar to Virginia 

 points strongly to a Rhsetic and Jurassic age for these plants. 



In the Triassic column of the table we find four species, or 9 per cent , 

 that show some affinity with Triassic plants. These are Schizoneura Vir- 

 giniensis, Mertensides distans, Asterocarpus platyrachis, and Acrostichides rJiom- 

 bifolius. Three of these show an equally close affinity with Rhsetic forms. 

 Schizoneura Virginiensis may be compared with S. Meriani of the Trias and 

 S. hcerensis of the Rhsetic, for both of these latter are probably the same 

 species. Mertensides distans resembles Pecopteris gracilis, Heer, of the Trias, 

 and also Gleichenites microphallus, Presl, of the Rhsetic. These two species 

 are also probably the same. Acrostichides rhombifolius resembles Neuropteris 

 Schcenleiniana, Schimp., of the Trias, and Cyclopteris pachyrachis of the Rhsetic. 

 We have, then, only one plant in the Virginia Mesozoic which has a greater 

 affinity with a Triassic form than any other; this is Asterocarpus platyrachis, 

 which is nearer A. Meriani than any other form. This degree of resemblance 

 in the list is very small, and would be fully accounted for by the survival 

 of plants of the Triassic flora. 



Three identical, and five allied species, or 19 per cent., find their rep- 

 resentatives in the Jurassic formation. The Jurassic element of this flora is, 

 then, much stronger than the Triassic, even without counting the plants of 

 Jurassic generic type found in the species peculiar to Virginia. 



We find four species identical with Rhsetic forms and eight allied to 



