MAMMALS. 377 



known species. It leads an aquatic, burrowing life, and feeds upon worms 

 and small aquatic animals, using its bill as does a duck. 



Family ECHIDNID^:. Beak elongate, toothless ; tongue elongate, ver- 

 miform ; body with strong spines among the hair. Echidna, with three 

 species from Australia, New Guinea, and Tasmania, has all the toes clawed. 

 In Acanthoglossns, from New Guinea, there are claws on but three toes, 

 and the beak is longer. All of these spiny ant-eaters are burrowing animals, 

 feeding chiefly upon ants. Echidna occurs as a fossil in the Australian 

 pleistocene. 



FIG. 356. Duckbill, Ornithorhynckus paradoxus, from Liitken. . 



The earliest fossil mammals yet found occur in the triassic 

 of North Carolina, South Africa, and Germany. Little is 

 known of them except of their jaws and teeth. Allied forms 

 are more abundant in later rocks, and some of them persist 

 until the eocene. From peculiarities of the teeth, which pre- 

 sent certain resemblances to the embryonic teeth of Omitho- 

 rJiyncJius, these fossils are sometimes placed as members of the 

 Prototheria, an example followed here ; although they also 

 present resemblances to the marsupials. 



ORDER II. PROTODONTA. 



Incisors reduced, molars with compressed cutting crowns 

 and undivided roots. Represented only by lower jaws of Droma- 

 therium and Microconodon from the American Jurassic. 



ORDER III. MULTITUBERCULATA (ALLOTHERIA). 



Incisors enlarged, molars tuberculate with distinct roots. In 

 these forms, which are represented by several genera, the teeth 



