Abstract
The author studied variations in the tooth size and morphology of Japanese shrewmoles, Urotrichus talpoides. Specimens were collected in Kawakami-Mura, Abu-Gun, Yamaguchi Prefecture, Honshu and on Mishima Island which lies in the Japan Sea about 46.3km off the northerncoast of the southwestern Honshu Island.The results obtained are summarized as follows:The mean values of tooth sizes (mesiodistal crown diameter, buccolingual crown diameter andrectangle) were larger in the Mishima specimens than those from Kawakami for most of the teeth. Regional size differences were larger in the anterior teeth and premolars that had simple occlusalrelation ships than molars that had complex occlusal relationships.The tooth morphology of the Mishima specimens was characterized by a considerable developmentof the cingulum and ridge. In degrees of development of the cinglum and ridge, continuous individualvariations were observed. From these facts, the author supports the cingulum theory that new cuspsdifferentiate from the original cingulum or ridge.It is surmisable that the specifications of tooth size and morphology in the Mishima specimenswere influenced by the peculiar habitat in Mishima Island, where neither natural enemies nor rivalspecies of mammals are present.
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