748 BIOLOGY OF THE SEAS OF THE U.S.S.R. 



desmarestioides) off the Californian coast ; and the fifth (E. cookeri) off the 

 coast of Peru. Four species of the genus Pelvetia are similarly distributed. 

 P. typica is found along both Asian and American coasts of the temperate 

 region. P. wrightii lives off the Japanese coast, while P. galapagensis is found 

 only in the Galapagos Islands, and P. canaliculata off the western and northern 

 coasts of Europe. The species mentioned are an example not only of amphi- 

 Pacific but also of amphi-boreal and bipolar distribution. 



A. P. Andriashev (1939) gives a large number of examples of the amphi- 

 Pacific distribution of fish. Two different sub-species of sardines (Sardinops 

 sagax) live off the American and Asian coasts; the anchovy (Engraoulis) 

 members of the family Osmeridae Hypomesus and Spirinchus, Cololabis saira, 

 many flatfish, and others have the same distribution. From this point of view 

 the distribution of the Pacific endemic family Embiotocidaeis most interesting. 

 This family is represented by 19 species (of 18 genera) off the coast of America. 

 Only two species (Ditrema and Neoditrema) live on the western side of the 

 Ocean. Many examples are known among Porifera, Polychaeta, Crustacea, 

 Echinodermata and Mollusca. 



Andriashev indicates identical species, closely related sub-species, and 

 among the amphi-Pacific forms species and even genera differing by the degree 

 of the discontinuity of their habitats in the north. Moreover, the habitats of 

 a series of amphi-Pacific organisms on the American coast do not extend 

 farther north than Oregon-Californian waters, and on the western coast no 

 farther north than the Sea of Japan. There can be only one explanation for 

 this distribution — both amphi-boreal and amphi- Atlantic : 'the geological 

 history of the northern part of the Pacific is comparatively short. Conditions 

 allowing a partial exchange of forms between the two different faunas — 

 American and Asian — occurred at many different times. At the site of the 

 contemporary fault in the region of the Bering Sea conditions were often, and 

 at different geological periods, very favourable, allowing some individual 

 elements of the two different faunas to spread northwards and to cross over 

 to the opposite sides' (A. P. Andriashev, 1939). Such openings no doubt 

 occurred periodically, beginning in the upper Miocene and especially during 

 the Pliocene, and later during the two inter glacial warm periods. Andriashev 

 rightly notes also that 'when the northern part of the Bering Sea was dry land, 

 the warm branches of the Kuroshio current had a more intense warming effect 

 [on its waters — L.Z.]'. 



All groups of the flora and fauna of the northern part of the Pacific are char- 

 acterized by their great mass development and their marked amphi-boreal 

 distribution. However, as a whole, the flora and fauna of both oceans differ 

 greatly. Thus the amphi-boreal organisms of the population of both oceans 

 alien to its original population belong to a young and newly arrived element. 

 It becomes evident, moreover, that some amphi-boreal groups are of Atlantic 

 origin (among the fish the family Gadidae, among the marine mammals 

 Phocidae) while others, much more numerous, are of Pacific origin (pleuro- 

 nectiforms among fish, Laminaria among sea-weeds). 



Amphi-boreal organisms are represented mostly either by identical or by 

 very similar sub-species and species ; this bears evidence of their comparatively 



