In this paper, the zoogeographical distribution of the Japanese soleoid fishes has been quantitatively investigated. The faunal characteristic of this group of fish at various representative localities extending from Japan to its adjoining region is first analysed by making use of SCHENCK et KEEN' method.
The central latitude of each sole is represented by the mean velue of the northern and southern limits expressed by the geographical latitude. The biological latitude of each representative locality is the mean of the central latitudes of several species found there. The latitudinal change of the distributional index (D•1), which is the difference between the geographical and biological latitudes, is described as the faunal characteristic of each locality.
The results obtained in this study are summarized as follows:
1. Based upon the central latitudes, the Japanese soles are made up of 3 forms, tropical, subtropical and temperate. Thus, the fish of which the central latitude is lower than 20 is called herein tropical form, which is represented by 7 species in Soleidae and 3 ones in Cynoglossidae. The subtropical form, defined here as one of which the latitude is about 30, contains 2 species in Soleidae and 5 ones in Cynogrossidae. The remaining 2 species of each family belong to the temperate form, of which the latituds is always higher than 33 (Tab. 1).
2. The latitudinal change of D•I in the Japanese soles found from Singapore or Kai to Muroran Prov. of Hokkaido or Uladivostok seems to be rather gradual, except for sudden change which takes place between Owashi (Mie Pref.) and Numazu (Shizuoka Pref.), and Hainan and Amoi, respectively (Fig. 2).
3. The point where the value of D•I becomes 0 is found to exist in latitudes 22°N in the Pacific and 27°N in the China Sea.
