CISTUDA. 



17 



Fam. IL EMYD.^ (or Emydidcc.) 



Pedes palmati, digitis distinctis, unguibus 5-4 longe acu- 

 minatis, nares pervii, mandibulee corneee. Testa depressa, 

 scutellis cornels tecta ; scutella marginalia 23-27, caudalia 

 distincta, sterni 11 vel 12. 



The head of these animals is rather depressed and shielded; 

 the neck is contractile into the body of the shell. The feet 

 are depressed and expanded, with separate toes united toge- 

 ther by a distinct web, and armed with sharp and rather long 

 claws ; the tail is usually more or less exposed. The shell is 

 generally depressed and solid, with a distinct bony margin, and 

 covered with horny plates ; the dorsal plates 13, with twelve 

 pairs of marginal plates, the caudal pair being separated by 

 a distinct suture, and with a narrow nuchal one. The 

 sterno -costal commissure is generally long, and usually fur- 

 nished with a distinct and rather large axillary and inguinal 

 plate. The sternum has eleven or twelve shields, the gular 

 pair being sometimes united, but never, as in the next family, 

 having an extra plate between them. The vertebrae of the 

 neck bend in a perpendicular bow, and the bones of the 

 pelvis are only attached to the vertebrae, and not to the 

 bones of the sternum. They hve in ponds and ditches, in 

 warm and temperate climates ; are rapid in their motions ; 

 eat mollusca, worms, insects and carrion, and only take their 

 food while in water : the eggs are oval and white. I have 

 observed 36 species ; 18 of which have come from America, 

 and 14 from the old world. 



The external characters to distinguish the sexes of these 

 animals have not been satisfactorily made out. Dr. Harlan 

 observes, that the females of some species are more keeled 

 than the males. The concavity of the sternum, which only 

 occurs in the first genus, does not appear to be peculiar to 

 the males; as Mr. Sowerby, Zool. Jour. ii. 485, says that 

 he has found eggs in the body of a specimen of Cistuda 

 Carolina which had a very concave sternum. 



Gen. 1. CISTUDA. [Box Terrapin.) 



Sternum latum, extremitatibus rotundatis, symphysi liga- 

 mentosa testae dorsali adnexum, in duos lobos per suturam 

 transversam medio divisum, scutella 12. 



D 



