Mr. Bell on a fossil Species of Chelydra. 381 



an appellation which it has derived from its general form, especially the 

 deeply carinated tail, as well as from its predatory habits. It is strictly a 

 freshwater form, and is highly carnivorous, seizing its living prey with great 

 avidity, and with a sudden snapping movement; to which circumstance it 

 owes its common name. Its food consists of young water-fowl, fish and 

 aquatic reptiles; and the length of the neck, the strength of the jaws, and 

 the robust and sharp claws with which the feet are armed, are admirably 

 adapted for seizing and tearing its prey. I have observed in several speci- 

 mens which I have kept living, that when teazed they will remain for a time 

 motionless, the head withdrawn underneath the shell, until, at a convenient 

 moment, the head is thrown forwards by an instantaneous extension of the 

 neck, and the object of its attack seized by a sharp sudden snap of the jaws. 

 I have seen a stick nearly as large as the little finger snapped in two by this 

 sudden movement. 



It frequently wanders to a considerable distance from the lakes in which it 

 habitually resides, and is said to hybernate either in mud or in the ground 

 near the water. A specimen which I possessed last year repeatedly endea- 

 voured to dig a retreat for itself in soft earth, which it removed by its fore 

 feet with great rapidity, entirely concealing itself in the space of a few minutes. 

 The whole of the freshwater forms are strikingly contrasted with those of the 

 terrestrial group, in the ease and rapidity of their movements, and in their 

 carnivorous habits, for the enjoyment of which these qualities are essentially 

 required ; and the group to which the present genus belongs may be con- 

 sidered as possessing those powers and habits in the greatest degree, with 

 the exception, perhaps, of the family of the Trionychidce, which, however, if 

 they exceed the former in the quickness of their motions, must yield to tbem 

 in strength. 



3 D 2 



