50 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



Time will not allow me to weigh all the points of agreement and 

 difference present in the axial skeletons of the representative mem- 

 bers of these two orders ; and I must limit myself to the expression 

 that the difference appears to me so great that, in view of them, it 

 is difficult not to regard the association of Ichthyopterygia and Sau- 

 ropterygia in one subclass as a taxical convenience, rather than as 

 expressive of a direct common ancestry. For such common ancestor 

 it would be requisite to go very far back. Gegenbaur hints that 

 the Enaliosauria came off from the vertebrate stem before the 

 Batrachia (Labyrinthodonta). 



The confusion which, for some time at least, almost invariably fol- 

 lows the dissolution of a generally accepted taxis, and the convenience 

 of the association of the two orders, recommend the present retention 

 of this subclass ; and upon a review of all the evidence, the zoological 

 position assigned to Enaliosauria after Amphibia by Prof. R. Owen 

 appears to be the best yet proposed. 



In our rocks the order Ichthyopterygia is, as already mentioned, 

 represented, I believe, only by the genus Ichthyosaurus ; for the 

 propodial * bone on which Prof. H. G. Seeley founded the Ichthyo- 

 sauroid genus Celarthrosaurus (C. Walkeri) agrees so closely with 

 the humerus of Platycarjpus, Cope, in those very points wherein 

 it deviates from the Ichthyosaurian pattern, that I think Cetar- 

 throsaurus should be removed from Ichthyosauria into Cope's sub- 

 class Pythonomorpha. In saying this I must guard myself against 

 being understood to imply that I regard this subclass as a valid one. 

 In North -American rocks the Ichthyopterygia include Sauranodon, 

 Marsh, which has a close general resemblance to Ichthyosaurus, but 

 is remarkable for being toothless. 



The geographical distribution of Ichthyosaurus was very wide. 

 Remains of one species were brought home by the North Polar 

 Expedition under Sir E. Belcher from the islands between West 

 Cornwall and North Devon, and vertebrae with portions of paddles 

 of two very distinct species were discovered in Spitzbergen by the 

 Swedish Expeditions in 1864 and 1868, under A. E. Nordenskiold ; 

 while fossils in the British Museum and in the Museum at Christ- 

 church, New Zealand, attest the occurrence of the genus as far south as 

 the 45th parallel of south latitude. In Europe the number of species, 

 as of individuals, appears to have been very great. It is probable, 

 however, that a critical review would much reduce them ; for there 

 is great difficulty in seizing upon good specific characters. These 

 Thos. Hawkins found in the shape and number of the mesopodial 

 (carpal or tarsal)bones and phalanges ; and on this basis he constructed 

 the singular nomenclature used in the l Book of the Great Sea-Dra- 

 gons ' and the ■ Memoirs of Ichthyosauri and Plesiosauri,' a no- 

 menclature not the least wonderful of the many singularities to be 

 found in those very remarkable folios. The uncouthness of such 

 words as Chiroparamehostinus, Chirostrongulostinus, Chiroligostinus, 

 Chiropolyostinus was so repellent that it cannot surprise us that 

 they never secured acceptance. 



* The term applied by Prof. O. 0. Marsh indifferently to the humerus and 

 femur. 



