TURTLES. 83 



for the beautifully mottled horny shields of its shell, which are the sole source of 

 the tortoise-shell of commerce. In its young state, the hawksbill may be readily 

 distinguished from the preceding species by the circumstance that the horny 

 shields on the back of the three-ridged shell overlap one another like the tiles on a 

 roof. With advancing age the shields gradually, however, become smooth, and in 

 very old specimens they meet at their edges, as in other members of the order. 

 At all ages the hinder margin of the carapace is more or less strongly serrated ; 

 and the compressed and sharply hooked beak will always serve to distinguish at a 

 glance a hawksbill from a green turtle. Moreover, the limbs always have two 



HAWKSBILL TURTLES SWIMMING (-^ Hat. size). 



claws. In the adult, the shields of the carapace are beautifully marbled and 

 mottled with yellow and dark reddish brown, while the plastron is yellow, and the 

 shields on the head and paddles are brown with yellow margins. In size this 

 species is somewhat inferior to the green turtle, the carapace attaining a length of 

 about 32 inches, against 42 inches in the. latter. In habits the hawksbill differs 

 markedly from the green turtle, being exclusively carnivorous. 



Loggerhead The third, and probably the largest species of turtle, is the 



Turtle. loggerhead (Thalassochelys caretta), easily recognised by its enormous 



head and the presence of at least five costal shields on each side of the carapace, 



which differs from that of the two preceding species by becoming completely 



ossified in the adult state. The beak is strongly hooked ; and while in the young 



