258 Isthmus Barriers Separating Fish Faunas 



Shhvo district itself, wliich is distinctly tropical and contrasts 

 strongly with that of the inshore bays behind it. This warm 

 " Black Current," analogous to our Gulf Stream, has its origin 

 in part from a return current from the east which passes west- 

 ward through Hawaii, in part from a current which passes be- 

 tween Celebes and New Guinea. It moves northward by way 

 of Luzon and Formosa, touching the east shores of the Japa- 

 nese islands Kiusiu and vShikoku, to the main island of Hondo, 



Fig. 17S. — Sacramento Perch, Archoplites interrwptus Girard. Family Centrarchidm. 



Sacramento River. 



flooding the bays of Kagoshima and Kochi, of AVaka, Suruga, 

 and Sagami. The projecting headlands reach out into it and 

 the fauna of their rock-pools is distinctly tropical as far to the 

 northward as Tokio. 



These promontories of Hondo, Waka, Ise, Izu, Misaki, and 

 Awa have essentially the same types of fishes as are found on 

 the reefs of tropical Polynesia. The warmth of the off-shore 

 currents gives tlie fauna of Misaki its astonishing richness, and 

 the wealth of life is by no means confined to the fishes. Corals, 

 crustaceans, worms, and mollusks show the same generous pro- 

 fusion of species. 



A fifth faunal area, closely related to that of the Black Cur- 

 rent, is formed by the volcanic and coral reefs of the Riu Kiu 

 Archipelago. This fauna, so far as known, is essentially East 

 Indian, the genera and most of the species being entirely iden- 

 tical with those of the islands about Java and Celebes. 



