OCTOBEE 11, 1901.] 



SCIENCE. 



549 



EFFECTS OF DIRECTION OF SHORE LINE. 



We may first note that a continuous 

 shore-line produces a mingling of fish- 

 faunas only when not' interrupted by bar- 

 riers due to climate. A north and south 

 coast-line, like that of the East Pacific, 

 however unbroken, permits great faunal 

 differences. It is crossed by the different 

 zones of temperature. An east and west 

 shore-line lies in the same temperature. 

 In all cases of the kind which now exist on 

 the earth (the Mediterranean, the Gulf of 

 Mexico, the Caribbean Sea, the shores of 

 India), even species will extend their range 

 as far as the shoreline goes. The obvious 

 reason is because such a shore-line rarely 

 ofiers any important barrier to distribu- 

 tion, checking dispersion of species. We 

 may, therefore, consider the age and nature 

 of the Isthmus of Suez and the character of 

 the faunas it separates. 



NUMBERS OF GENERA IN DIFFERENT FAUNAS. 



For our purposes, the genera must be 

 rigidly defined, a separate name being used 

 in case of each definable difference in struc- 

 ture. The wide-ranging genera of the 

 earlier systematists were practically cosmo- 

 politan, and their distribution teaches us 

 little. Using the modern definition of 

 genus, we find in Japan 483 genera of ma- 

 rine fishes ; in the Red Sea, 225 ; in the Med- 

 iterranean, 231. In New Zealand 150 are 

 recorded ; in Hawaii, 171 ; 357 from the 

 West Indies, 187 from the Pacific coast of 

 tropical America, 300 from India, 450 from 

 the East-Indian islands and 427 from Aus- 

 tralia. 



Of the 483 genera ascribed to Japan, 156 

 are common to the Mediterranean also, 188 

 to the West Indies and Japan, 169 to the 

 Pacific coast of the United States and 

 Mexico. With Hawaii Japan shares 90 

 genera, with New Zealand 62 ; 204 are 

 common to Japan and India, 148 to Japan 

 and the Red Sea, most of these being found 



in India also. 200 genera are common to 

 Japan and Australia. 



AFFINITIES OF JAPANESE FAUNA. 



From this, it is evident that Japan and 

 the Mediterranean have much iu common, 

 but apparently not more than Japan shares 

 with other tropical regions. Japan natur- 

 ally shows most likeness to India, and next 

 to this to the Red Sea. Proportionately 

 less is the resemblance to Australia, and 

 the likeness to the Mediterranean seems 

 much the same as that to the West Indies, 

 or to the Pacific coast of America. 



But, to make these comparisons just and 

 effective, we should consider not the fish 

 fauna as a whole ; we should limit our dis- 

 cussion solely to the forms of equatorial 

 origin. From the fauna of Japan we may 

 eliminate all the genera of Alaskan- Aleu- 

 tian origin, as these could not be found in 

 the other regions under comparison. We 

 should eliminate all pelagic and all deep- 

 sea forms, for the laws which govern the 

 distribution of these are very different 

 from those controlling the shore fishes, and 

 most of the genera have reached a kind 

 of equilibrium over the world. 



SIGNIFICANCE OF RARE FORMS. 



We may note also, as a source of confu- 

 sion in our investigation, that numerous 

 forms found in Japan and elsewhere are 

 very rarely taken, and their real distribu- 

 tion is unknown. Some of these will be 

 found to have, in some unexpected quarter, 

 their real center of dispersion. In fact, 

 since these pages were written, I have taken 

 in Hawaii representatives of three* genera 

 which I had enumerated as belonging chiefly 

 to Japan and the West Indies. Such species 

 may inhabit oceanic plateaus, and find many 

 halting places in their circuit of the tropical 

 oceans. We have already discovered that 



* Antigonia, Etelis, EminelicMhys. 



