494 EIGHTH PACIFIC SCIENCE CONGRESS 



makes an exception of the general rule that shallow water fauna has 

 narrower distribution ranges than deep water fauna. 



Most of the molluscs of Japanese bays have their chief distribution 

 area in the Asiatic continent, and they may properly be said to belong 

 to the fauna of continental coast. The ranges of their distribution 

 often cover the coast of south eastern Asia, the China seas including the 

 west coast of Formosa, the Japanese Islands including Hokkaido, and 

 the Russian Maritime Province. 



These continental elements are historically the descendants of the 

 fauna of Pleistocene, when the Japanese Islands were more closely con- 

 nected with the Asiatic continent than at present. The physiological 

 basis for the wide range of distribution may have been acquired through 

 the life in the euryhaline and eurythermal habitat of the bay. 



As members of this fauna may be mentioned the following species, 

 most of which being dominant members of benthic molluscan com- 

 munities of Japanese bays. 



Raeta pulchella: Japan incl. Hokkaido, Siam, Borneo, Russian 



Maritime Province. 

 Brachidontes sennousia: Japan incl. Hokkaido, Central China, 



Korea, Russian Maritime Province. 

 Theora luhrica: Japan incl. Hokkaido; represented by a closely 



related species in Southeastern Asia. 

 Paphia undulata: Japan, Siam, China; represented also by a closel»y 



allied species P. textrix in the continent. 

 Anomia cytaeum (A. lischkei): Japan incl. Hokkaido, China, west 



coast of Formosa. 

 Venerupis japonica (formerly misidentified as V. philippinarum): 

 Japan incl. Hokkaido, China, Formosa, Korea; represented by 

 V. indica in southeastern Asia. 

 Caecella chinensis: Japan incl. Hokkaido, China. 

 Zirfaea japonica: Japan incl. Hokkaido, China; represented by a 



closely allied species Z. dilatata in the continent. 

 Mactra sulcataria: Japan incl. Hokkaido, China coast. 

 Laternula limicola: Japan incl. Hokkaido, China, Saghalien. 

 Ostea gigas: Japan incl. Hokkaido, China, west coast of Formosa, 



Russian Maritime Province. 

 Littorina brevicula: Japan incl. Hokkaido, China, Korea, Russian 



Maritime Province. 

 Veverita didyma: Japan incl. Hokkaido, China. 

 Mitrella bella: Japan incl. Hokkaido, China. 

 The similar tendency of wide distribution is recognised in the estua- 

 rine and brackish water molluscs, though sometimes replaced by closely 



