g6 BAUR. [Vol. I. 



The question now is, from which group of Reptiles descended 

 the Ichthyopterygia ? 



The skull shows characters of the Rhynchocephalia, the 

 oldest Crocodiles (Belodon) and the Dinosaurs ; but it is still 

 more generalized than in these groups. This is proved espe- 

 cially by tvvo bones, — the opisthotic and the supratemporal. 



The opisthotic is separate as in the Testudinata.' 



Huxley^ speaks of a flattened bone between the postorbital, 

 postfrontal, and the squamosal ; this bone (temporal, Cuvier — 

 prosquamosal, Owen), according to Huxley, does not appear to 

 have any precise homologue among other Reptilia. 



I shall show, in another paper, that this peculiar " bone is 

 nothing else than the supratemporal " of the Lacertilia, and the 

 " squamosal " of the Stegocephali ; that the " squamosal " of 

 the Stegocephali is really the supratemporal, the " supra- 

 temporal " of the Stegocephali, the squamosal, of the Reptilia. 



The Ichthyopterygia, therefore, are the only Reptiles, so far 

 as now known, which have a supratemporal, like that of the old 

 Stegocephali. 



Another character common to the Rhynchocephalia, a few 

 Lizards and Dinosauria, the oldest Crocodilia (Belodon), and 

 Sauropterygia,^ is the presence of the postorbital and the post- 

 frontal in a separate condition. 



The scapular arch of the Ichthyopterygia is Lacertilian or 

 Rhynchocephalian. 



The ribs are two-headed, like those of the Crocodilia, 

 Dinosauria, etc. They are different from the ribs of all other 

 known Reptiles, because they are never connected with the 

 neurapophyses ; they never leave the body of the vertebra 

 (according to Owen's figures). 



Abdominal ribs are developed, as in the Rhynchocephalia and 

 Sauropterygia. 



Therefore we have combined characters of the Rhynchoce- 

 phalia, the oldest Crocodilia and Sauropterygia. To-day we 

 do not know a group of Reptiles showing such characters; 



' Cope, E. D. On the homologies of some of the cranial bones of Reptilia, and 

 on the systematic arrangement of the class. 



Proc. Amer. Assoc. Adv. Sc, Vol. xix., p. 199. 1871. 



- Huxley, T. H. A manual of the anatomy of vertebrated animals. London, 

 1 87 1, p. 246. 



' In Simosaurm these two bones have already united. 



