144 



ANIMAL BIOLOGY 



can have any difficulty in knowing a member of this order. 

 The subdivision of the order into families is not so easy, 

 however, and the popular attempts to classify chelonians 

 as turtles, tortoises, and terrapins have not been entirely 

 successful. Species with a vaulted shell and imperfectly 

 webbed toes and strictly terrestrial habits are called tor- 

 toises. Species with flattened shells and strictly aquatic 

 habits should be called terrapins {e.g. mud terrapin). They 

 have three instead of two joints in the middle toe of each 

 foot. The term turtle may be applied to species which are 

 partly terrestrial and partly aquatic (e.g. snapping turtle 

 (Fig. 271)). - Usage, however, is by no means uniform. 



FIG. 271. SNAPPING TURTLE (Chefydra serpentina). 



Most reptiles eat animal food ; green terrapins and some 

 land tortoises eat vegetable food. Would you judge that 

 carnivorous chelonians catch very active prey ? 



The fierce snapping turtle, found in ponds and streams, 

 sometimes has a body three feet long. Its head and tail 

 are very large and cannot be withdrawn into the shell. 

 It is carnivorous and has great strength of jaw. It has 

 been known to snap a large stick in two. The box tortoise 

 is yellowish brown with blotches of yellow, and like its 

 close kinsman, the pond turtle of Europe (Fig. 266), with- 

 draws itself and closes its shell completely. Both lids of the 

 plastron are movable, a peculiarity belonging to these two 

 species. The giant tortoise of the Galapagos Islands, ac- 



