306 SYNOPSIS OF THE VERTEBKATE FAUNA OF THE PDERCO SERIES. 



row, with an iiitermarginal series of scuta, and without fontanelle. Surfaces not 

 sculptured. 



Chelydra crassa sp. nov. Dermatemys sp. Cope ; Proc. Amer. Phil. Soc, 1883, p. 461. 



This species is represented in my collection by fragments of two individuals. 

 Of the typical specimen there are preserved, two vertebral, nine marginal, and three 

 plastral bones; of the second, three vertebral bones. The specimens indicate 

 an animal of the average size of the existing snapping turtle, Chelydra serpentina. 



The bones of both carapace and plastron are relatively much thicker than the 

 corresponding parts of the snapping tortoise, equaling in this respect the largest 

 existing sj^ecies of Emys. The bridge of the plastron is not so slender as in C. ser- 

 pentina. The vertebral bones have a median keel-like angle, which becomes at the 

 anterior part of each vertebral scutum a pi-ominent rib. This results from the abrupt 

 depression of the suiface on each side immediately posterior to the transverse dermal 

 suture. In the lai'ger specimen this suture is deeply notched anteriorly, and its 

 anterior border is so prominent posteriorly as to give an imbricate appearance, the 

 anterior vertebral scute rolling over the posterior by an obtuse border. The marginals 

 of the bridge are very massive, and the pit for the process of the costal is at one side 

 of the middle, and is nearly round. It is flat in the C. serpentina. The pits for the 

 plastral fingers are three, on the inner inferior edge of each marginal, and are directed 

 obliquely. The external foce of the marginals is distinguished by a rabbet, the in- 

 ferior margin of which projects as a ridge beyond the external face. Inferior face 

 convex. No other except the fine mutual sutures on the marginals of the bridge. 

 The free marginals, of which I have two, and one of them the anal, have no gomphosis 

 nor suture with the costals or pygal, being held in place by the integuments and by 

 the mutual marginal sutures. The dermal scuta are well marked, the marginals having 

 theii- bounding suture below that of the marginal bones. Surface of the shell every- 

 where smooth. 



Measurements. 



No. 1. Inch. 



AntcropnsUTior dianictev of vertebral bone 8 



r anteroposterior 83 



Diameters of marginal of bridge I transverse (greatest) 35 



[ vertical 98 



anteroposterior 13 



s ver 



[ transverse 43 



( intoriorh' 1 00 



anteroposterior { , 



i medially 4d 



transverse (witliout gomphosis) 1-90 



vertical (at middle) 23 



Diameters of anal marginal i vertical 35 



Diameters of hyosternal ■ 



