78 TORTOISES AND TURTLES. 



brown or blackish, while the head and neck are brown with yellowish spots. 

 From other species of the genus it is distinguished by the large size of the plastron, 

 in which the anterior lobe is narrower than the mouth of the shell. 



In general habits the mud-terrapins seem to be very similar to the fresh- water 

 members of the tortoise family, although they prefer swamps and marshes to 

 running waters. Carnivorous in their diet, they subsist chiefly on small fishes, 

 insects, and worms, while they have been observed to capture newts. They will 

 readily take a baited hook, and when thus caught sink rapidly and heavily to the 

 bottom, thus causing the angler to believe that he has hooked a weighty fish. At 

 the commencement of winter they bury themselves in moss, where they remain 

 dormant till the following May. An extinct genus nearly allied to the mud- 

 tortoises occurs in the Tertiary rocks of Baden. 



Maw's terrapin (Dermatemys mawi) may be taken as a good 

 representative of the second family, all the three genera of which are 

 restricted to Central America. This family connects the preceding one with the 

 snappers, agreeing with the latter in the presence of an entoplastral bone, and with 

 the former in the characters of the vertebrae of the short tail, which have the cup in 

 front, and the absence of a roof to the temporal fossa of the skull. Maw's terrapin 

 and its allies further agree with the mud-terrapins in the incompleteness of the 

 series of neural bones of the carapace ; the hinder ones being wanting, and thus 

 allowing the costal plates to meet in the middle line. Externally, the members of 

 the present family may be distinguished from the Testudinidce by the presence 

 of an additional series of infra-marginal shields between the marginals and those 

 of the plastron a feature which they possess in common with the big-headed 

 tortoise and the snappers. Maw's terrapin, which attains a length of some 

 15 inches, and is the sole representative of its genus, has the plastron large, and 

 connected with the carapace by an elongated bridge ; the gular shield being single, 

 and the usual five other pairs of shields being present on the plastron. Unlike 

 most other tortoises, there are twelve pairs of marginal shields, in place of the 

 usual eleven. In the other two genera of the family Staurotypus and Claudius 

 the plastron is reduced to a cross-like shape, and has but a short connection with 

 the carapace ; while the number of paired shields on the former is only four or 

 or three, and the chin is provided with a pair of wattle-like appendages, of which 

 there is no trace in Maw's terrapin. While in the two species of Staurotypus the 

 plastron is connected with the carapace by a bony bridge, in the single represen- 

 tative of Claudius the junction is entirely ligamentous. This family is represented 

 by several extinct genera in the Tertiary and Cretaceous strata of North America, 

 one of which (Baptemys) had the full series of neural bones; and there appear 

 to have been allied forms in the European Tertiaries. 



THE SNAPPERS AND ALLIGATOR-TERRAPINS. 

 Family CHELYDRID^l. 



Resembling the big-headed tortoise in the great relative size of their hook- 

 beaked heads, and their elongated scaly tails, the snappers and alligator-terrapins 



