MONOGIÎAPH or JAPANESE OPHIUKOmEA. 365 



boundary between the two elements is better marked on the 

 Pacific side than on that of the Sea of Japan. The Hraits of the 

 zone of contact are approximately 33^. and 38J. parallels on 

 the Pacific side, and 80. and 43. parallels on the side of the Sea 

 of Japan. The axis of the zone of contact is very nearly 36. 

 parallel, which has been stated by Claek to be the line of contact 

 between his Bering and Honshu faunae. 



The two groups of Honshu- American and Honshu species 

 are evidently heterogeneous. For example, Amphlpholis imgetana, 

 Amphiura carchara, Gorgonocephalus tuberosus, G. dolicliodactylus, 

 Ophiolehcs hrachijgnatha, 0. asaphes, 0. tuherosa, Ophiosemnotes 

 œdldisca, Opliiopliolis mirabilis, 0, bracliyactis, Stegophiura striata, 

 St. vivipara, St. sculpta, St. sterea, St. brachyactis, St. sladeni, &c, 

 may be derivatives of the Arctic fauna, while the rest are largely 

 derivatives of the tropical, especially Indo-Pacific, fauna. 



Claek has recognised scarcely a dozen species which 

 occur in both the East Indian and Japanese regions. As a 

 result of the present study, I recognise sixty-one species, or more 

 than one-fourth of the total number of Japanese species, that 

 occur also in the East Indian region. On the other hand, the 

 boundary between Claek's Bering and Honshu fauna) well coin- 

 cides with that between my Arctic, chiefly Bering, and tropical, 

 chiefly Indo-Pacific or East Indian, elements. Thus, I am led to 

 look upon the Honshu fauna not as a perfectly distinct one, but 

 to be a terminal section of the Indo-Pacific, or East Indian, 

 fauna. 



The known northern limits of several more typical, httoral 

 Indo-Pacific species are shown in the accompanying chart. 



