SWAMPS AND SHORES 479 



from the salt marshes and river mouths out to sea, and accordingly 

 have a wide distribution. The African crocodile may also enter the 

 sea, and has reached Madagascar. A few small lizards* frequent the 

 beach to feed on invertebrate refuse and small crabs. 



Two groups of marine turtles are breeding members of the com- 

 munities of the ocean shores. One of these is the primitive "leather- 

 back" turtle (Dermochelys coriacea), which may weigh up to a ton, 

 the largest of all chelonians. This is cosmopolitan in distribution in 

 tropical seas, but is rare everywhere, least so in the west Atlantic 

 from Florida to Brazil and in the Indian Ocean. It breeds on the 

 coasts of Brazil, the Tortugas, and the Bahama Islands. Only juvenile 

 and mature forms are known, for they visit land only for breeding 

 purposes and otherwise lead a pelagic life. The other family repre- 

 sented is the Chelonidae which includes the green or edible turtle 

 (Chelonia my das) , the hawksbill, Ch. imbricata, and the loggerhead 

 turtle (Caretta). The first is a plant-feeding animal and is therefore 

 restricted to littoral waters; the others feed on fishes and mollusks. 

 The breeding season of the green turtle varies in different parts of the 

 world. In the East and the West Indies it breeds from April to June; 

 on the west coast of Africa the breeding season is from September to 

 January. Other wide-ranging tropical and subtropical animals show 

 similar nonconformities in breeding time in different parts of their 

 ranges. The loggerhead turtle ranges further north and is an occasional 

 visitor on European coasts as far as Belgium. All these sea turtles 

 deposit their eggs in excavations made on sandy shores. 



The mammals of the seacoast include the polar bear, sea otter, sea 

 lions, seals, walruses, manatees, and dugongs, besides the more casual 

 visitors. The concentration of these amphibious mammals, manatees 

 and dugongs excepted, is notably arctic and antarctic, with almost 

 continuous connecting colonies on the west coast of the Americas, 

 where the upwelling cold waters produce suitable temperature and food 

 conditions. Semi-marine mammals are otherwise notably absent in the 

 tropics, though the completely marine whales abound, and the exist- 

 ing sirenians are confined to shallow coastal waters and rivers in the 

 warm zones. 



The polar bear of the Arctic is a land or ice animal, but it is a 

 powerful swimmer; since its principal food is seals, it is almost con- 

 fined to the ice border and pack ice, where the seals occur. It is circum- 

 polar, and entirely without a south polar representative. The sea otter, 

 which has been almost completely exterminated for its incomparable 



* The iguanid, Tropidurus, and the skinks, Crypt oblcpharus and Emoia. 



