CHELYDRlDiE. 



223 



bone, and no excavation for the hyoplastron; also in having the free border of the seventh 

 peripheral much more obtuse and the upper border not in sutural contact with the costal; 

 further, in having a single process on the free border of the ninth peripheral. 



284. 



Figs. 282-285. Macrochelys floridana. Peripherals of type. X. 



282. Fourth left peripheral, with section across middle of length. 



283. Seventh right peripheral seen from above, with section across middle of length. 



284. Seventh right peripheral seen from below. 



285. Ninth right peripheral seen from above, with section near hinder end. 



Genus CHELYDRA Schweigger. 



No supramarginal scutes. Orbit directed outward and upward. Tail with large scutes 

 interiorly (Boulenger). 



This genus is represented in North America, in a fossil state, only by the following species. 

 Cope's Chelydra crassa will be described under the genus Hoplochelys. 



Chelydra serpentina Linnaeus. 



TestuJo serpentina, Linnaeus, Syst. Nat., ed. x, 1858, p. 199. 



Chelydra serpentina, Schweigger, Prod., 1814, p. 23. Boulenger, Cat. Chelonians, 1889, p. 20, 

 figs. 3, 4. 



Cope (Extinct Batrachia, Reptilia and Aves of North America 1869, p. 125) reports 

 briefly that Samuel R. Harrison, of Easton, Maryland, had found remains of this species in 

 Pleistocene deposits at Oxford Neck, Talbot County, Maryland. They were accompanied 

 by bones of Elephas amencanus, Cervus canadensis, Cariacus virginianius, and Terrapene 

 eurypygia. 



Family DERMATEMYDID^ Gray. 



Plastron in most cases suturally articulated to the carapace; with an entoplastron, but 

 without mesoplastra; the anterior and posterior lobes usually reduced in size. Nuchal bone 

 with or without costiform processes. Neural bones reduced in number, except in Baptemys; 

 some of the hinder costal bones meeting their fellows in the midline, except in the same genus. 

 Peripheral bones in 10 or 11 pairs. Plastron furnisht with a full series of inframarginal 

 scutes, except in Basilemys. The scutes of the anterior lobe perhaps in all cases modified 

 from the condition seen in Baena. Caudal vertebrae in all the known forms procoelous. The 

 hinder lobe of the plastron often with a scar for the pelvis, but the latter never suturally joined 

 to the plastron. Temporal region not rooft over and no parieto-squamosal arch. Quadrate 

 notcht behind for the stapedial rod. 



