Isthmus Barriers Separating Fish Faunas 259 



Resemblance of the Japanese and Mediterranean Fish Faunas. 

 It has been noted by Dr. Giinther that the fish fauna of Japan 

 bears a marked resemblance to that of the Mediterranean. 

 This likeness is shown in the actual identity of genera and 

 species, and in their relation to each other. This resemblance 

 he proposes to explain by the hypothesis that at some recent 

 period the two regions, Japan and the Mediterranean, have been 

 united by a continuous shore-line. The far-reaching character 

 of this hypothesis demands a careful examination of the data 

 on which it rests. 



The resemblance of the two faunal areas, so far as fishes are 

 concerned, may be stated as follows : There are certain genera * 

 of shore fishes, tropical or semi-tropical, common to the Medi- 

 terranean and Japan, and wanting to California, Panama, and 

 the West Indies, and in most cases to Polynesia also. Besides 

 these, certain others found in deeper water (100 to 200 fathoms) 

 are common to the two areas, f and have been rarely taken 

 elsewhere. 



Significance of Resemblance. The significance of these facts 

 can be shown only by a fuller analysis of the fauna in ques- 

 tion, and those of other tropical and semi-tropical waters. If 

 the resemblances are merely casual, or if the resemblances 

 are shown by other regions, the hypothesis of shore continuity 

 would be unnecessary or untenable. It is tenable if the resem- 

 blances are so great as to be accounted for in no other way. 



Of the genera regarded as common, only twoj or three are 

 represented in the two regions by identical species, and these 

 have a very wide distribution in the warm seas. Of the others, 

 nearly all range to India, to the Cape of Good Hope, to Australia, 

 or to Brazil. They may have ranged farther in the past ; they 

 may even range farther at present. Not one is confined to the 

 two districts in question. As equally great resemblances exist 

 between Japan and Australia or Japan and the West Indies, 

 the case is not self-evident without fuller comparison. I shall 



* Of these, the principal ones are Oxystomus, Myrus, Pagrus, Sparus, Macror- 

 hamphosus, Cepola, Callionymus, Zeus, Uranoscopus, Lepidotrigla, Chelidonich- 

 thys. 



f Among these are Beryx, Helicolenus, Lotella, Nettastoma, Centrolo pints, 

 Hoplostethus, Aulopus, Chlorophthalmus, Lophotes. 



J Beryx, Hoplostethus. 



