40 ONYCHIOPSIS. 



on tte general character of tlie fructification, and not on details 

 of sporangial structure. Unfortunately no sporangia are sufficiently 

 clearly preserved to afford that important assistance which a 

 more intimate knowledge of them would give. It is to be 

 regretted that the material from the English Wealden does not 

 often enable us to learn anything as to histological structure. 

 There is, however, a notable exception in Tempskya ScUmperi, 

 Corda, in which structural details have often been more or less 

 clearly mineralized, thus enabling us to add something towards the 

 elucidation of the real botanical position of this remarkable fossil. 



A. Genera assigned to existing Families. 

 Order LEPTOSPOEANGIAT^. 

 The Sporangia, with walls composed of a single layer of cells, 

 are developed from single surface cells. 



Family POLTPODIACE^. 



Sporangia stalked, and with a vertical incomplete annulus. 



Genus ONYCHIOPSIS, Tokoyama. 

 [Joum. Coll. Sci. Japan, vol. iii. 1890, p. 26.] 



Trond tripinnate, main rachis slender, may be winged, pinnae 

 alternate, approximate, lanceolate. Pinnules narrow, lanceolate, 

 acute, alternate, the larger ones serrate, and gradually passing into 

 pinnules with narrow ultimate segments. Fertile pinnse 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. 



This genus was instituted by Tokoyama for the reception of 

 a Japanese species, originally described by Geyler ' as Thyrsopteris 

 elongata, and afterwards referred to by Tokoyama as Dicksonia 

 elongata. The occurrence of fertile pinnules of a distinct and 

 unusual type led to the removal of the specimens from Thyrsopteris 

 to Onychiopsis. Tokoyama pointed out the resemblance between 

 the fertile pinnse of the Japanese specimens and those of the 



' Palaeontographica, vol. xxiv. 1876-77, p. 224, pi. xxxi. fig. 4. 



