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Annals of the Carnegie Museum. 



various genera, for the greater part but imperfectly known. More- 

 over these Thalassemyds compose the group, which has been considered 

 to stand most nearly in an ancestral relationship to the existing marine 

 turtles, previous to my demonstration of the structure of the Pro- 

 pleurinse of the New Jersey Cretaceous, and proof that this primitive 

 littoral subfamily includes the forms which virtually bridge the gap 

 between primitive land tortoises and the existing genera of the Chelo- 

 ninae. On the other hand it is to be emphasized that several other 



Fig. 5. Osteopygis gibbi Wieland, X §-• Plastral view. Primitive semi-marine 

 turtle from the New Jersey Cretaceous, showing the elongate and in-turned epiplastra 

 characteristic of the Cheloniid^e. The horn shields are not indicated, but are in 

 approximate agreement with Thalassochelys. 



Cretaceous subfamilies besides the Protosteginae are so different from 

 the New Jersey forms, that their ancestry must still be sought for 

 amongst the Thalassemyds. Such are in particular the Desmato- 

 chelydina?. It is hence more and more strongly suggested, as the 



