Turciculid Gastropoda of Japan

Sixteen turciculid gastropod species, Recent and fossil are described from Japan. Those species are distributed among one genus Turcicula and the four subgenera; Turcicula s.s, Bathybembix, Ginebis and Gonvexia. The last mentioned subgenus is newly proposed and Ginebis is redefined and discussed, because of the confusion concerning its classification. Foreign and allied species of Turcicula are remarked based upon the nomenclature. In the classification of the species, letter formulae are proposed for the external morphological characters. It is noteworthy that the biogeographical distribution of the group is recognized at the subgeneric level. Prior to Pliocene, the species of the subgenus Turcicula had been known only from the Japan Sea side (Japan Sea Type), but these are found on the Pacific Ocean side of Japan from Pliocene to Recent. On the contrary, the species belonging to the subgenera, Bathybembix, Ginebis and Convexia were previousely known only from the Pacific Ocean side of Japan through the geological past to Recent and have been known as the Pacific Ocean Type. From the Recent distribution of the subgenus Ginebis, the Pacific Ocean side of Japan can be classified into two provinces; the northern and the southern being separated at the sea off Boso Peninsula, middle Honshu. Phylogenetically, though more data are needed, the origin of some stocks are now estimated based upon their external morphological development. Fossil turciculid gastropods might be important for geological interpretation especially of the paleogeography and the development of their tubercles are useful for ecological analysis of the sediments deposited off shore or on the continental slope.