Summary and Conxlusion ' 



(1) The coefficient of closeness {y) of marine MuUusca is connected 

 with the latitude [x) in the following equation, 



log y ^ a X -\- b, 

 where a and b are constants. When a given locality is taken as a centre, 



log y = a {x — ^o) , 

 where a'o is the latitude at the central locality, and a is defined as a 

 decreasing constant of common species. Practically in the Pacific Coast 

 a = J:: 0-134, being (+) for southern localities and ( — ) for northern 

 localities from the centre. 



(2) The latitudinal value in the flat fishes is parallel to the coefficient 

 of closeness in marine Mollusca, and these animal groups have a common 

 ecological type ; from these facts a similar mode of geographical distri- 

 bution are reasoned in these animal groups. 



(3) The type of distribution shows no significant difference between 

 the Pacific and the Japan Sea coasts, and Soya and Iturup Island are 

 distinguished from this type. From these facts it is estimated that the 

 northern limit of this type of distribution is lat. 43-44° N. and the 

 southern limit is lat. 26-27° N. in the Japanese coasts having the centre 

 at lat. 35° N. 



(4) The coefficient of closeness and the latitudinal value are 

 respectively a characteristic index to show a fauriistic change from 

 locality to locality ; however, the former is rather superior to the latter 

 in respects of possibility to compare the difference among localities and 

 to estimate the type of geographical distribution, in the case of which 

 the northern and southern limits are difficult to decide in the geographical 

 distribution of animals. And, further, the expression of decrease of the 

 coefficient of closeness from the centre to distant localities is superior 

 to that of geographical division into provinces expediently by reason 

 of the distribution of several characteristic species. 



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