Chap. II. 



THE CIIELYOID^. 



339 



111 the fresh state, this cavity is prolonged by a memljranoiis snout, as in Trion^-x. 

 The lower jaw is thin, excejiting at the condyles, where it is thickened on the inner 

 side to a nearly spherical form ; the articulating ball projects somewhat higher than 

 the upper edge, l)ut it is lower than the lower edge of the jaw just before it; 

 it rolls by a broad and long convex surface on the articulating surface above. 

 The jaw rises forward to the coronal angle, where it is so high and broad that 

 its upper edge rises above the top of that part of the skull which it incloses ; 

 from the angle forward it is small and lilunt, and fits closely into the alveolar 

 depression above. The tongue bones are largeh" developed, and make a broad, 

 firm floor under the cavity of the mouth. 



Most of the man}- peculiarities of the head are clearly connected with the 

 form of the mouth, and thus with the kind of food, and manner of catching 

 and devouring it. The jaws are weak, and neither pointed nor sharp-edged ; and 

 therefore unfit for catching large, active prej^, or tearing any tough v^egetable or 

 animal matter. The mouth is broad but very close, when its roof and floor are 

 brought near together; it seems on that accoimt best fitted for catching and 

 swallowing minute animals. The mode of articulating of the lower jaw, and the 

 large size of the depression in the mastoids for the digastric muscle, indicate 

 perhaps that the jaws are opened and shut quickly and continuously with a 

 movement somewhat Hke that of a duck's bill. The legs are strong, and the 

 feet broad and compact, with long, sharp claws. 



This family contains a single genus, well known luider the name of Chelys. It 

 embraces only a single species, called Matamata in tropical South America, where it 

 is common. Its habits are httle known. From the resemblance of this Turtle 

 to the Chelydroidaj and the Trionychida?, I am inclined, however, to infer that, 

 like these, it lays spherical eggs. 



The family first described by Fitzinger under the name of Hj-draspides^ was 

 soon afterwards united, by J. E. Gray,^ with the ChelyoidiV) ; but I believe this to 

 be a mistake,^ if I am permitted to express an opinion after having had so few 



' Fitzinger, Syst. Rept., 1S43, 8vo. 



2 J. E. Gray, Cat. Urit. Mus., 1844, 8vo. 



' It lias already been remarked in a note, p. 335, 

 that the Turtles united as one natural group under 

 the names of Clielidida^ or Klodites Pleuroderes, do 

 not constitute a natural familj-, but embrace a number 

 of families, linked together by the peculiar structure 

 of the neek, and besi<les by the close connection lie- 

 tween the pelvis and the carapace and plastron. Of 

 these families I have only been able to examine the 



Chelyoida; proper with suificient precision to ascer- 

 tain fully their family characters. I take, however, 

 this opportunitj- to call the attention of herpetologists 

 to the differences I have thus far noticed among the 

 other groups. I have already stated above, that, as 

 the ChelyoidiB proper recall the Chelydroida', the 

 Stemothaeroida; form in the same manner the coun- 

 terpart of the Cinosternoida;, while Pelomedusa and 

 Pentonyx remind us of the true EmydoidiC. The Hy- 

 draspides, restricted to the genera riatemys, Rhine- 



