CHAPTER XV.

ISTHMUS BARRIERS SEPARATING FISH FAUNAS.

The Isthmus of Suez.--The Fish Fauna of Japan.--Fresh-water Faunas of Japan.--Faunal Areas of Marine Fishes of Japan.--Resemblance of Japanese and Mediterranean Fish Faunas.--Significance of Resemblances.--Differences between Japanese and Mediterranean Fish Faunas.--Source of Faunal Resemblances.--Effects of Direction of Shore Lines.--Numbers of Genera in Different Faunas.--Significance of Rare Forms.--Distribution of Shore-fishes.--Extension of Indian Fauna.--The Isthmus of Suez as a Barrier to Distribution.--Geological Evidences of Submergence of Isthmus of Suez.--The Cape of Good Hope as a Barrier to Fishes.--Relations of Japan to the Mediterranean Explained by Present Conditions.--The Isthmus of Panama as a Barrier to Distribution.--Unlikeness of Species on the Shores of the Isthmus of Panama.--Views of Dr. Günther on the Isthmus of Panama.--Catalogue of Fishes of Panama.--Conclusions of Evermann & Jenkins.--Conclusions of Dr. Hill.--Final Hypothesis as to Panama. 255