CHEWNIA 241 



nor great prowess; and perhaps the formidable beak was used more 

 in social quarrels than for food-getting. That these marine turtles 

 departed from the usual reptiUan habit of laying their eggs upon 

 land is improbable. The tortoise shell turtles of the Bahamas lay 

 three or four hundred eggs in a hollow scooped out in the sand and 

 then leave the young to their own devices; certainly many a 

 one is gobbled up by birds of prey or other enemies on their way 

 to the water. Perhaps the young Archelon lost its hind leg in 

 some such mishap. 



LEATHER-BACK MARINE TURTLES 



The most remarkable member of the Chelonia now hving is 

 Dermochelys coriacea (Fig. 128), the great leathery or leather-back 

 turtle of the warmer parts of the Atlantic, Indian, and Pacific 

 oceans, the sole member of the family Dermochelydidae. It is 

 the largest of all living turtles and the most thoroughly aquatic 

 of all, whether living or extinct. It sometimes reaches a length 

 of six feet, or half that of the largest known extinct forms, and 

 weighs a thousand or more pounds. Agassiz saw a specimen that 

 he said weighed a ton. Unlike other turtles, it has a carapace quite 

 pecuhar to itself, composed of a layer of thin, irregularly polyg- 

 onal bones forming a mosaic, completely hidden in the thick skin, 

 and entirely free from the skeletal bones beneath them. The 

 larger of these skin bones form seven rows above, which appear 

 in the living animal as sharp keels running the whole length of 

 the shell. On the under side there are five rows of smaller-sized 

 bones, under which there are vestiges of bones representing the 

 normal plastron of turtles. The hmbs are powerful, flattened 

 paddles, not unlike those of Eretmochelys, but whoUy destitute of 

 claws. The front paddles are much larger than the hind ones; 

 the humerus is long and flattened, and the digits are elongated. 

 The leather-back is a powerful and effective swimmer, going long 

 distances. Its habits are not well known; its food is chiefly fish, 

 crustaceans, and mollusks. 



So very different is the structure of its shell that some excellent 

 naturahsts regard Dermochelys as the equivalent in rank of all other 

 turtles combined, the sole representative of the suborder Athecae, 



