44 chloLOGY. 



was represented in the record by Proganochelys (Psammochelys), a 



highly specialized form belonging to the Pleurodira, from the Upper 

 Trias of Europe, as well as by others (Chelyzoon) of true cryptodiran 



Fig. 340. — A Triassic dinosaur of the Connecticut valley, Anchisaurus colurus, restored 

 by Marsh, one-thirtieth of natural size. 



affinities from the middle Trias, 1 indicating, by their divergence and 

 specialization, a much earlier origin of the chelonian order. 



The advent of the non-placental mammals. — Of peculiar interest 

 is the appearance of early forms of non-placental mammals. They 

 were small, and so primitive in type, that it is not altogether certain 

 that they were not mammal-like theromorphs. They are regarded, 

 however, as prototherian mammals, allied to the monotreines and 

 marsupials. The remains are fragmentary, teeth being the most 

 significant portions preserved. These show relations to the therio- 

 donts, and perhaps point to them as the source of descent, though 

 this is far from certain. Two genera are recognized in America 



1 Recently described bv von Huene. 



