CuAP. II. THE CINOSTERNOIDyE. 347 



to the Stei'iiotlia^rina of Bell. As the .name of that group is derived from the 

 genus Terrapene, J/c/-., which at that time was restricted ]>y Gray to the common 

 Cistudo of the United States, it applies as little to the family of Cinosternoida; 

 as that of Bell. Major LeConte, in his late attempt to classify the Testudinata,^ 

 has als(j perceived the impropriety of leaving the genera Staurotypus and Cino.s- 

 terniim among the true Emydoidai, and placed them in liis second family with 

 Chelydra. Were not the Trionychida} also embraced by him in that family, this 

 change would have constituted, in my opinion, one of the most important improve- 

 ments recently introduced in the classification of the Testudinata, for Cinosternum 

 and Stain-otypus are as renaote from the true Emydoidaj as Chelydra itself, and 

 more closely allied to Chelydra than to any other family among the Amyd*, 

 though they constitute also a distinct family, the characters of wdiich now follow. 



The body is long and narrow. The flattened part of the lower surface upon 

 which it rests is much larger than in the Chelydroidaj, occupying at least one half 

 of the width across the middle, and continuing broad forward, between the shoul- 

 ders, to its front end, and backward, under the pelvis and hip joints, to its hind 

 end, so that the space between it and the projecting outer edge of the body 

 above is much less in this family. The outer edge of the bod}- is not nearly 

 as high at the front end as in the Chelydroida;, yet it descends steeply to about 

 midway, but keeps upon nearly the same level around the hind end. The upper 

 surfiice rises along its middle line, from the front end to tlie middle of the bod}- 

 and be}-ond, to near the seventh dorsal vertebra, from whence it falls steeply 

 to the hind end ; consequently the bodj^ is highe.st far back of a transverse 

 section tln-ough the middle of the body ; and as the hind end is as broad, or 

 broader, than the front, the bulk of the body is also thrown backward. The.se 

 peculiarities will always clearly distinguish the carapace of this family from the 

 shed-roof of the ChelydroidiB, or the more regularly ai'died cuirass of the Em^•- 

 doida\ As the outer edge fixlls from the front end backward, while the middle 

 line rises, the upper surface, in order to reach the margin, has to descend far 

 down on either side, except about the front end, and, as the body is never wide, 

 it must descend steeply. The outer edge of the carapace is raised, all round, 

 considerably above the lower flattened surface of the body. It meets the pla.s- 

 tron. and is sutured to it along the two marginal plates which correspond to the 

 third anil fourth ribs, and is there slightly turned inward and downward ; but 

 from this suture, either way about the ends of the body, it projects free, a little 

 distance beyond the attached surface, and flares outward. 



The free edges of the plastron, that is. the outer edges, where not joined to 



' Proc. Acad. Xat. Sc. of I'liiladelphia, 1854. 



