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Chap. III. GENERA OF CINOSTERNOIDiE. 423 



miiul)ers several genera, and that its representatives are not all, as the celebrated 

 naturalists of Leyden believe, varieties of only two species of tlie genus Emys. 

 Of the groups thus distinguished as genera, there are three in the sub-family 

 of Cinosternoids proper, namely, Cinosteruura, Thyrosternum, and Platythyra ; and 

 three in the sub-family of Ozothecoids, namely, Goniochelys, Ozotheca, and Stau- 

 rotypus. Tlie colors prevailing in all these Turtles are dark, here and there 

 enlivened by reddish or greenish or yellowish tints. 



GENERA OF THE SUB-FA^^LY OF OZOTIIECOID.E. 



Besides the Mexican genus Staurotypus, this sub-family embraces two genera 

 that have representatives within the limits of the United States. 



I. Goniochelys, Aff. The jaws are very strong, and their muscles powerful. The 

 strength of the upper jaw lies in the thickness of the bone ; that of the lower 

 jaw lies both in the thickness of the bone and the height of the jaw itself. 

 To give room for the large muscles, the head is very broad across the fossae 

 temporales. The sides of the head, back of the eye, spread wide apart down- 

 ward ; the roof, between the orbits, is broad, but still they spread apart down- 

 ward, and therefore open somewhat upward. The sides of the nose curve a little 

 outward in passing down from the top. The jaw, under the eye, is very thick ; 

 its outer surface curves outward, and then again turns sharply inward to the alve- 

 olar edge ; under the sides of the nose that surface slants also far inward ; 

 while at the front end it slants backward, but not so much as it does at the 

 sides. At the symphysis the jaw is drawn down more or less, and often consid- 

 erably, to a point or a chisel edge. The horizontal alveolar surface is very broad, 

 leaving but a small space within its angle. The lower jaw is both thick and 

 high ; it is drawn upward at the symphysis to a strong point ; its outer surface 

 slants far inward from the alveolar edge at the sides, and backward at tlie end. 

 The alveolar surfice, as in the upper jaw, is very broad, and leaves Ijut little 

 space within its angle ; it is broadest at the symphysis, and its inner edge curves 

 somewhat inward in passing back to the hind end. It is nearly Hat from side 

 to side just before the angle, luit has a ridge descending on to it from the 

 angle. The scales of the shield have a marked tendency to imbrication. 



Goniochelys tkiquetka, A[/. Thus far this species has only been foiuid in Lake 

 Concordia, in Louisiana. I am indebted for specimens to Prof Baird, Mr. B. 

 Chase, and Prof. Wailes. Severid specimens from the same source are preserved 

 in the Mu.seum of tlie Essex Listitute in Salem. The mo.st prominent specific 

 character consists in the very sharp and high keel of the back, and the tlat side.s, 



