CLASS REPTILIA. 



before acute, behind acutely nicked ; head brown, yellow 

 lined on each side. North America. 



IV. Sternum very narrow, cross-shaped, rounded at 

 both ends, united to the hack shell by very long bony processes. 

 Sternal plates Jive pair, and a pair over the symphysis. 

 Chelydra Schw. 



Serrated Alligator Tortoise. Emys (Chelydra) Serpen- 

 tina. Test. Serrata, Penn. Chelydra Lacertina, Schw. 

 Young. Test. Serpentina. Lin. Shaw, t, 29. 



Shell oblong ; vertebral shields flat ; upper edge of costal 

 plates, prominent ; behind bluntly six toothed. Young 

 sharply three-keeled and toothed. North America. 



III.— Chelys, Gray. 



Feet palmated ; claws five — four, sharp ; nostrils sub-tubu- 

 lar ; shell solid, covered with horny plates ; hinder pair of 

 marginal plates separate ; sternal plates thirteen, with an 

 intergular one ; neck contractile on the side ; pelvis attached 

 to the sternum and vertebrae. 



I. Lips horny ; sternum front, and sometim,es hinder 

 lobes mobile ; intergular plate marginal. Sternotherus, 

 Bell (part.) Gray.* 



Chestnut Chelys. Ch. (Sternotherus) Casfaneus, Gray. 

 Emys Castaneus, Schw. Testudo Subniger, /3 Daud. 

 Sternotherus Castaneus, Bell. Zool. Jour. t. 14. 



Shell oval, sharply keeled, convex, chestnut ; shields 

 radiately rugose ; areola black. Var. /3 hinder lobe, mobile. 



* I have used as the name of the sub-genera those which have been 

 given by authors to what they considered genera in this family; but I 

 have generally restricted their signification, so as to render them more 

 definite. 



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