AND AVES OF NORTH AMERICA. 



131 



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prcssion in the form of both humerus and femur, and decided by this test, the genera 

 following are all Chelydroid Emydidae. 



The metatarsals of the hind foot preserved, indicate a broad natatory member more 

 like those of Trionyx than those of Chelydra. 



At the same time the vertebral derma] scutes have the most narrowed form character- 

 istic of various genera of Emydidae. The femur has a slender curved shaft as in Chely- 

 dra and Chelys. The sternum is more that of Chelydra than of the sea turtles. This is 

 seen in the narrowness of the stcrno-carapacial bridge, which is very wide in Chelone, 

 and very narrow in Chelydra. In the; cretaceous genera, the width is intermediate, and 

 the hyo and hyposternal bones are united medially, and are not merely prolonged ante- 

 riorly and posteriorly as in Chelone. The lateral sternal regions were therefore less pro- 

 tected than in the sea turtles, while the general small size and form of the sternal hones 

 also point to the cross-shaped plastron of Chelydra. 



It does not offer any approach to the Pleurodira, since the xiphistcrnum is free from 

 the pelvis. The cranium of the genus Euelastes, which belongs here, shows the techni- 

 cal details of the Cheloniidac, with the form of head, physiognomy, and no doubt, the 

 carnivorous adaptations of Chelydra. In the genus Ostcopygis, also of the cretaceous, 

 the characters diverge still more from those of the modern sea turtles. Here five margi- 

 nals in front and three behind, are united with the; disc. The anterior marginal scutum 

 becomes united with the first vertebral. In other respects the characters are those of 

 Propleura. In Eytoloma the marginals arc free as in Chelone. 



Several genera have been discovered in the lithographic slates and other strata of the 

 Jurassic period in Germany, Switzerland and France. These; have been described by 

 Minister, Wagner,* arid Von Meyer. f Some of these are allied to Chelone, but the 

 majority of them appear to me to have a near relationship to Chelydra, and to those 

 herein described. This has been scarcely alluded to by the learned authors quoted, and 

 in general their affinities to existing forms have been but obscurely indicated. Those 

 which 1 would refer to this neighborhood are: 



ElJRYSTERNUM MiillSt. 



E. wagleri Miiust. 



E. crassipes Wagn. (Palaeomedusa 



Mey.) 

 E. redtenbacheri (Aciclielys Mey.) 

 [DIOCHELTS Mey. 



I. fit/ingeri Mey. 



I. wagneri Mey. 

 Hydeopelta Mey. 



II. meyeri Thioll. 

 Platychelys Wagn. 



P. oberndorferi Wagn. 



* Abhandl. d. m. pli. cl. K. Bayerisoh Acad. Wiss. IX. 



t Reptilien o d. Lithograph. Schicfcr. 



