308 POPULAR HISTORY OF THE xiQUARIUM. 



up, capable of floating. My friend has frequently observed 

 this shell in use by the Frogs as a boat ; several remaining 

 upon it at the same time, and moving it by their overhanging 

 legs and arms ! 



Emydid^. 

 Fresh-water Tortoises, -which spend their time in and 

 about the margins of lakes and rivers, have (as compared 

 \yith land tortoises) forms well adapted for the requirements 

 of their existence. The shell is flatter, and the openings 

 for the limbs are wider, to allow of the freer action required 

 for swimming. The feet are more slender and rather flat- 

 tened. The toes are expanded and connected by a mem- 

 brane. The claws are long and sharp, to enable them to 

 seize and tear their prey, which consists of aquatic animals. 

 In short, on seeing an Emi/s of the true typical form, you 

 at once recognize a creature formed to paddle about and 

 take his prey in the waters; while he can, with equal facility, 

 crawl about on the banks or sun himself upon any rocky 

 elevation within his reach. One family of Fresh-water Tor- 

 toises, the TrionycliidcE, are remarkable for having their 

 whole body covered with a strong coriaceous skin, instead 

 of the horny plates which usually cover the bony box in 



