Devonohelicoceras hidaense, a new torticonic oncocerid (Cephalopoda) from the Lower Devonian of Central Japan

Abstract

Based on the four specimens from the Lower Devonian (Emsian?) D4 Member of the Fukuji Formation, and a specimen from an unknown locality, a new genus and species of the oncocerid cephalopod, Devonohelicoceras hidaense, is described as the second known oncocerid from Japan. The present genus is most similar to the Late Silurian genus Foersteoceras, but differs in its weakly depressed whorl section, submarginal siphuncle with positional shifting, and well-developed actinosiphonate deposits. It is likely that the actinosiphonate deposits functioned as a substratum of adhesive liquid which has a lower specific gravity than the sea water.

(Communicated by Tatsuro MATSUMOTO, M. J. A., Sept. 12, 2003)