272 Systematic Faleontologt 



rank. The published drawings of these forms, especially the enlarged 

 pinnules showing detail, are for the most part inaccurate and idealized 

 to such an extent, or are composites so that even the experts in the 

 National Museum often find it impossible to decide which specimens 

 represent Fontaine's drawings. 



With regard to our taking up the genus OnycMopsis of the Polypodi- 

 acege rather than Thyrsopteris of the Cyatheaceas it may be said that 

 while Thyrsopteris, as a strictly form-genus, may not be open to any 

 great degree to criticism, it implies a relationship with the existing 

 species which the evidence does not substantiate, so that the best modern 

 usage refers the older types of this sort to the genus Coniopieris Bron- 

 gniart, and the later ones to this genus Onychiopsis. It is quite possible 

 that the modern genus Thyrsopteris was a prominent Jurassic and older 

 Cretaceous type, there being many parallel cases, as, for example, the 

 gymnospermous genus Ginkgo. Some of the evidence is at least suffi- 

 cient to prove that forms named Thyrsopteris are referable to the family 

 Cyatheacese, so that in considering the Potomac forms we have to decide 

 whether the fact that the Jurassic forms like Thyrsopteris Maahiana and 

 Thyrsopteris Murrayana of Heer are members of the Cyatheace^ shall be 

 given greater or less weight than the fact that the same type of sterile 

 frond very abundant in the Lower Cretaceous from England to Japan 

 has fertile pinnules like those of the genus Onychium of the Polypo- 

 diacese. It is true that only sterile pinnules are known from the 

 Potomac deposits, but the fertile parts have been found associated, and 

 in organic connection with these identical sterile pinnules in California, 

 Japan, England, Belgium (?), Bohemia, and Portugal. The writer 

 prefers to believe that the latter evidence is entitled to the greater weight. 

 The modern genus Onychium has several widely distributed, chiefly 

 tropical, species of Japan, China, India, Persia, Abyssinia, and the East 

 and West Indies. In this connection attention should be called to the 

 fertile specimens from Fredericksburg described as Aspleniopteris pin- 

 natifida, since this type which is referred to the Aspleniese is very similar 

 to the fertile pinnae of a specimen of Onychiopsis Gceppei-ti from Japan, 

 kindly communicated by Professor Yokoyama. 



