224 ANNALS NEW YORK ACADEMY OF SCIENCES 



higli mountains, affording less opportunity for expansional evolution of 

 the littoral fauna. The Antarctic continent appears equally unfavorable, 

 and dispersal from that center would also be hindered by the broad 

 stretches of ocean. 



We may expect, therefore, to find the littoral fauna of the North At- 

 lantic most progressive, that of the North Pacific less so, the tropical 

 faunae containing many relict types of discontinuous distribution, and 

 the Antarctic faunas partly composed of types from the north which had 

 crossed the barrier of warm water when the climatic zones were less 

 differentiated than they now are; partly of groups developed in the south. 

 Whether these groups were closely allied on the different southern con- 

 tinental shores would depend on their ability to cross the great barriers 

 of deep ocean that separate them. 



The distribution of the pinnipeds accords with these principles. The 

 most specialized family is the Phocidae, originating apparently in the 

 Atlantic-Arctic basin, where Phoca, the most progressive genus, is found 

 in the North Atlantic and Arctic seas and has penetrated into the North 

 Pacific as far as California and Japan. Southward in the Atlantic it is 

 succeeded by the less progressive Monaclius in the Mediterranean and 

 Antillean region. The Antarctic Phocidee are also primitive and archaic, 

 related more or less nearly to Monachus. In the Pliocene of Belgium 

 are found extinct genera closely related to Phoca and others more primi- 

 tive allied to Monachus. 



The walruses, also Arctic and North Atlantic, have penetrated into 

 the North Pacific only as far as Bering Sea; they are likewise recorded 

 from the Pliocene of Northern Europe and along the North Atlantic in 

 the Pleistocene as far south as Virginia. 



The third family, the Otariidse, is decidedly more primitive in struc- 

 ture, being less specialized for marine life. They are found in all the 

 southern seas and on the North Pacific coasts. They are unknown to 

 the North Atlantic and Arctic shores and have never been found fossil 

 in either Europe or eastern North America. Desmatophoca and Ponto- 

 leon of the Miocene of Oregon are perhaps ancestral types, but more 

 evidence is necessary before its North Pacific origin can be regarded as 

 satisfactorily indicated. 



INSECTIVOKA 



Among the Insectivora we deal with a number of very ancient races, 

 whose relationship is much more distant than in many other mammalian 

 orders. They are small, and most of the surviving members are scarce 

 and little known, while they are still less known as fossils. So far as 



