CHAPTER VI: THE BOX TURTLES 

 GENERA EMYS AND CISTUDO 



Turtles with Divided, Hinged Plastrons Descriptions of the 

 Species Their Habits. 



IN the consideration of the genera Emys and Cistudo, the 

 student has passed, in the classification of the Chelonia, the 

 strictly aquatic species, and is referred to the connecting links 

 between the former and the true tortoises terrestrial reptiles, 

 of Testudo and allied genera. The structure and habits of the 

 species of the present chapter afford admirable examples of 

 transition, in the scale of evolution. 



The Box Turtles derive their popular name from the struc- 

 ture of the plastron, which is attached to the carapace by an elas- 

 tic, cartilaginous joint. The plastron is divided by a central 

 hinge, which permits both the front and rear portions to be 

 drawn against the lower surface of the carapace. Thus, in time 

 of danger, the creature draws in the head and limbs and closes 

 the shell in box-like fashion. 



The genus Emys is composed of but two species, one of 

 which inhabits Europe and Asia and is very aquatic in habits. 

 The other species, Blanding's Turtle, occurs in the United States, 

 and although possessing fully webbed feet and being partial 

 to the neighborhood of water, is given to the habit of wandering 

 over swampy areas. The genus Cistudo is composed of five* 

 North American species that are strictly terrestrial although 

 several of these species display distinct traces of webs be- 

 tween the toes, while others have feet like the true tor- 

 toises. Thus we trace our way along the links of the 

 chain, and can understand why the species of Cistudo, al- 

 though quite terrestrial, cannot properly be termed tortoises, as 

 their structure demonstrates that they are more closely allied to 

 the turtles. 



* A sixth species occurs in Mexico C. mexicana. It has three claws 

 on the hind foot. 



54 



