CHELONIANS. 



THIRD FAMILY. Cinosternoida,- (Gr. xtyew, kineo, to move; 

 v, sternon.) MUD and MUSK TORTOISES. 



The Tortoises of this family have long and narrow bodies, 

 covered by a shield which is entirely ossified. The marginal 

 plates are twenty-four in number ; the plastron is divided into 

 three sections, and, " at least in the adult species, is made up of 

 eight plates, there being no odd one, as in all the other families 

 of the sub-order." (Ag.) The shield or carapace is covered 

 with large horny scales ; the head is large, elongated, and pyr- 

 arnydal in form ; the mandibles are hooked, and in the under 

 jaw covered with fleshy excrescences. In the female, the tail is 

 short ; in the males, thick and long. Their legs are slender, ill 

 fitted for land travel, but easily carrying the body through the 

 water over the bottom. As a family, they are dwarfish in their 

 forms, the largest not being more than nine inches long, and the 

 smallest not more than four inches. These Tortoises smell 

 strongly of musk. Their disposition is a blending of shyness 

 and ferocity. " They remind us," says Agassiz, " of the Insec- 

 tivora among the Mammalia, the rapacious habits of which are 

 in strange contrast with their size and feebleness." Their 

 movements are abrupt and quick, but have little power ; their 

 food is chiefly animal ; their habits aquatic, though sometimes 

 they bask in the sun on the shore. They lay only from three 

 to five eggs, having the shape of a lengthened ellipse with very 

 blunt ends, and a glazed, shining surface, much smoother than 

 that of the other turtles' eggs, and also quite thick and brittle. 



This" family, entirely American, is represented by the genera 

 Cinosternon and Sternotharus, (Gr. sternon; thairos, a hinge.) 

 The former has both the front and hind parts of the plastron 

 movable upon an intermediate fixed position ; the latter has the 

 plastron solid, with the front part movable. 



Cinosternon represents the MUD TORTOISES, or Cinosteroids. 

 Several species are described. 



C. Pennsylvanicum, or Thyrosternum, (Gr. thuron, porch ; 

 sternon,) Pennsylvanicum, (Ag.) is very common in various parts 

 of the United States. It inhabits ditches and muddy ponds, and 

 often takes the hook. Its food consists of frogs and small fishes. 

 The length is seven or eight inches. 



Sternothcerus, or Ozotheca, (Gr. ozo, to smell ; theke, repos- 

 itory,) Ag., of sub-family Qzothecoidce, includes the MUSK TOR- 

 TOISES. Of the species the Musk Tortoise, S. odoratus, or O. 

 odorata, Ag., is the most common and the smallest one known, being 



