TORTOISES AND TURTLES. 389 



or two longitudinal ridges. To this group belong the exclusively American 

 terrapins of the genus Chrysemys, some of which range as far south as Brazil 

 and Uruguay. Burma and Bengal are the respective habitats of two allied 

 terrapins constituting the genus Morenia, distinguished by certain features 

 in the conformation of the skull ; while the single representative of Ocadia 

 is Chinese. The four other genera, all the members of which are known as 

 batagurs, are confined to the Oriental countries, and include the largest 

 fresh-water members of the whole family, the shell of one of them measuring 

 as much as twenty inches in length. The batagurs, which are divided into 

 the genera Cachuga, Callagur, Batagur, and HardeUa, are specially char- 

 acterised by the excessive development of the vertical bony buttresses con- 

 necting the carapace with the plastron, which project as walls into the 

 interior of the shell in such a manner as to divide it into three imperfect com- 

 partments. The different genera are chiefly distinguished by the contour 

 of the vertebral horny shields of the carapace ; the fourth shield in one 

 genus narrowing anteriorly almost to a point in a manner quite unknown in 

 any other members of the order. The batagurs have shells of extraordinary 

 strength and solidity; and the larger species are almost exclusively aquatic, 

 and very numerous in the rivers of India and Burma. In spite of their 

 herbivorous habits, they are said to be dangerous to bathers ; and it is 

 certain that a snap from their powerful jaws would cause a very serious wound. 



A strange-looking aquatic tortoise (Platysternum megalocephaluni) from 

 the countries lying between Burma and the south of China demands specia 1 

 notice as being the sole representative of a family. Ex- 

 ternally, its most conspicuous features are the enormous Family 

 size of the head ; the hooked beak ; the extreme flatness of Platystemidce. 

 the shell, which looks as if it had no room to contain the 

 internal organs of the creature ; the great length of the scaly tapering tail ; 

 and the rather long and powerfully -clawed legs. The skull differs from that 

 of the Testudinidce in having the whole of its hinder portion covered over by 

 a bony roof ; and most of the vertebrae of the long tail articulate with one 

 another by means of a cup behind and a ball in front, instead of in the 

 reverse manner. These afford ample grounds for referring this tortoise to a 

 family apart. The whole length of the shell is only about six inches. Of 

 the habits of this remarkable reptile naturalists are ignorant. 



The mud-terrapins (Cinosternum), of which there are eleven species, all 

 inhabitants of America to the north of the Equator, alone represent a third 

 family, easily distinguished from all other Chelonia by the 

 absence of the unpaired entoplastral bone of the plastron, Mud-Terrapins, 

 thus reducing the number of elements in the lower shell Family Cino- 

 from nine to eight. The shell is depressed, with its two sternidce. 

 portions firmly united ; and the plastron has its two ex- 

 tremities movable, and its gular shields either united or absent. The tail is 

 very short ; and the webbed toes, save the fifth hind one, terminate in strong 

 claws. In habits, these terrapins resemble ordinary fresh- water species. 



Three small genera of terrapins from Central America, respectively named 

 Dermatemys, Staurotypus, and Claudius, form the fourth family. Together 

 with the Cinosternidce, these differ from the Testudinidce in 

 that each of the two lateral angles of the nuchal bone of Family Der- 

 the carapace gives off a long bony stay projecting backwards matemydida. 

 to underlie the marginal bones. The skull is of ordinary 

 form ; the plastron has the usual nine bones, and the tail is short. As in 



