Some Miocene Arcid Fossils from Japan Part 2, On Anadara kakehataensis and its Allies

Abstract

This paper deals with taxonomic and palaeontological studies of Anadara kakehataensis and its allies. The results are summarized as follows : 1. The specimens described as Anadara kurosedaniensis agree morphologically with the junior form of Anadara kakehataensis, so that the former is regarded as a synonym of the latter. 2. A. kakehataensis is not referable to Anadara but to Scapharca as to its subgenus. 3. Although the junior form of A. daitokudoensis is closely related to that of A. kakehataensis, A. daitokudoensis is distinct from A. kakehataensis in the shape of posterior slope and in the difference of number of rib, as far as the present specimens are concerned. 4. A. kakehataensis and its allies are found always associated with such shells as Vicarya, the dwellers of black mud in embayment under warm current. 5. They are classified into three types : A. daitokudoensis type, medium type (Yatsuo, Ayukawa) aud large type (Tokunari) of A. kakehataensis. Their junior forms have a similar shell to each other. They can be divisible only in adult form. This fact suggests that their form is the best adapted one to individual embayment which has different nutrition owing to it marine conditions.