TURTLES AND TORTOISES 17 



perate and tropical parts of the globe except Australia 

 and Papuasia. Its great variety of species range from 

 the persistently aquatic with their broadly webbed feet, 

 to the marsh-loving turtles, with which the webs are 

 imperfectly developed and finally to the tortoises — che- 

 lonians with club-shaped feet; all tortoises are strictly 

 terrestrial, some of them inhabiting the deserts. 



On all the species the shell is covered with horny 

 shields. With the majority the head may be completely 

 withdrawn into the shell. There are nine plastral bones. 



Two North American genera stand as typical in rep- 

 resenting the structure and habits of the semi-aquatic 

 species. These are: — 



Chrysemys and Malacoclemmys ; the American Ter- 

 rapins: We will adopt the general title of Terrapins 

 for the species of these genera, as many of the members 

 involved are sold in large numbers in the markets, where 

 they bring from moderate to very high prices, according 

 to their kind. All of the terrapins grow to a fair size, 

 having a shell from eight to fourteen inches long. Many 

 have the upper shell attractively marked while the head 

 and neck are vividly striped with yellow — or red. Of 

 all the North American terrapins the best known is 

 the Diamond-Back Terrapin, Malacoclemmys palustris, 

 which is a favorite and costly article of food. 



Genus Chrysemys: A great majority of the species 

 inhabit North America; the remainder occur in Mexico 

 and Central America. Of the fifteen North American 

 members of the genus, the Painted Terrapin, C. picta, 

 is thoroughly familiar. There can be no doubt about the 

 identity of this pretty creature : for the blackish or olive 

 upper shell with its yellow-bordered shields and the 

 striking vermilion bars and crescents on both upper and 

 lower series of marginal shields are strong distinguish- 



