STERNOTHERUS. 37 



Fam. ///.— CHELYD^, or ChelydidcE. 



Pedes palmati, digitis distinctis, unguibus 5-4 eloiigatis 

 iicuminatis ; nares tubulosi ; mandibulse plerumque cornese ; 

 testa depressa, scutis cornels tecta ; scutella marginalia 24-25, 

 caudalia distincta, sterni 13. 



The head much depressed and broad, covered with regular 

 large shields ; the neck long, broad, retractile under the side 

 of the shell, and not into the centre of it as in the Emydes, 

 the shell generally much depressed, the margin furnished with 

 a small nuchal plate, and the caudal pair always separated 

 by a distinct suture. The sternum is always attached to the 

 upper shell by a bony suture. The symphysis is rather short 

 and covered by the outer end of the pectoral and abdominal 

 plates. The axillary and inguinal plates are usually very small 

 and hidden by the margin. The sternal shields thirteen, the 

 additional or intergular plate being situated between the pair 

 of gular plates, or between the hinder angle of them and the 

 front angle of the humeral plates. The vertebrae of the neck 

 are so formed that the animal cannot withdraw the head into 

 the shell, like the other tortoises : and the bones of the pelvis 

 are united by a bony process to the hinder part of the ster- 

 num as well as to the vertebrae, as observed by Cuvier in the 

 skeleton of Chelys, (Os. Fos. v. 214, t. 12, f. 20) ; and by 

 Mr. Bell in Hydraspis. This character may be known even 

 when the pelvis is lost by the scar left by its attachment to 

 the bone. 



They live in ponds and ditches in the warm regions of 

 both Continents, eating MoUusca and worms, and feeding only 

 in the water. 



The animals of this group require further examination and 

 comparison. Of the sixteen species here indicated, two are 

 Australasian, five African, and nine Tropical American. 



Gen. 1. STERNOTHERUS, {Sternotherus.) 



Sternum latum, lobus anterior mobilis sutura transversa 

 ligamentosa ad lobum medium articulatus, scutellum inter- 

 gulare marginale, nuchale nullum, maxillge cornege. 



