322 PROCEEDINGS OF THE NATIONAL MUSEUM. tol. 41. 



Japanese Upper Jurassic or Neocomian species originally described 

 by Geyler as Thyrsopteris elongata and founded upon sterUe pinnules. 

 The discovery of fertile pinnules by Yokoyama led to the erection of 

 the present genus which is very close to the modern genus OnycMum 

 Kaulfuss, which is made a subgenus of Cryptogramme R. Brown by 

 Diels in Engler and Prantl's Natiirhchen Pflanzenfamilien (1899), 

 although there seems to be but shght warrant for Diel's treatment. 



Seward in working over the abundant Wealden material in the 

 British Museum found that the widespread species which usually 

 went by the name of Splienopteris mantelli Brongniart was congeneric 

 with Yokoyama's species mentioned above, and he therefore rede- 

 scribed Brongniart's species as Onychiopsis mantelli, redefining the 

 genus in the following terms :^ 



Frond tripinnate, main rachis slender, may be winged, pinnae alternate, approxi- 

 mate, lanceolate. Pinnules narrow, lanceolate, acute, alternate, the larger ones 

 serrate, and gradually passing into pinnules with narrow ultimate segments. Fertile 

 pinnae with alternate elliptical pinnules which differ in shape from the sterile pinnules 

 and have the sporangia on the lower surface, giving them the appearance of raised 

 elliptical bodies. 



The most abundant and characteristic ferns of the Potomac group 

 were referred by Professor Fontaine to Thyrsopteris Kuntze, an 

 existing monotypic genus of the family Cyatheacese inhabiting the 

 island of Juan Fernandez, Of these some 40 species, so called, were 

 described. They were all based on sterile fronds or parts of fronds, 

 often extremely small and inadequate fragments. Professor Fontaine, 

 after quoting Heer's diagnosis of Thyrsopteris ^ writes: 



This description, given by Heer for the genus Thyrsopteris, so far as the portion 

 pertaining to the sterile frond is concerned, agrees well with a large number of species 

 in the Potomac flora. These I place provisionally in the genus Thyrsopteris, on 

 account of the great resemblance that the shape of the pinnules, the lobing, and the 

 nervation show to the sterile forms of various species determined to be Thyrsopteris 

 by their fructification. As, however, no fructification is found in the Potomac species, 

 the placing of these plants in the genus must be regarded as provisional. It is quite 

 possible that some of them belong to Aspidium and Dicksonia. 



It should be noted that a number of the species of Thyrsopteris described in the 

 following pages show a good many features similar to those of Sphenopteris mantelli, as 

 described by Schenk and Heer (p. 120). 



Professor Fontaine does identify Sphenopteris mantelli from one 

 locality in the Potomac belt, that at Federal Hill, Baltimore, and in 

 discussing its bearing upon the age of the deposits he says: 



Now in the Potomac flora not only is S. mantelli present in beds which show plants 

 of the most recent facies existing in the formation, but there is a very important group 

 of ferns which, although placed in the genus Thyrsopteris, have nearly the nervation 

 and foliage typified in S. mantelli. The great development in the Potomac of ferns 

 of the general type of S. mantelli gives strong evidence of Wealden or somewhat later 

 age. A somewhat later age than Wealden is indicated, perhaps, as most of the species 



» Flora foss. Arct., vol. 4, pt. 2, 1877, p. 28. ! Seward, Wealden Flora, pt. 1, 1894. p. 40. 



