812. 北海道コニアシアン階上部から産出した Inoceramus (Cordiceramus) の新種について

抄録

In this paper, a new species Inoceramus (Cordiceramus) kawashitai is established. The specimens were occurred from the Upper Coniacian of the Oyubari, Ikushumbets and Obira areas of Hokkaido. The variation of selected characters are examined quantitatively on the basis of measurements and statistics, in addition to traditional observation. The average relative growth of two relations (shell height us. shell length and shell height us. breadth) are also examined. On the ground of its considerably inflated equivalve shell, subquadrate or pentagonal marginal outline and development of three radial ridges, this species is certainly assigned to the subgenus Cordiceramus. But the ontogenetic change of the certain characters does not agree with that of any known species. I point out the significance of the occurrence of Cordiceramus from the Upper Coniacian of Japan, in that it represents the lower part of the range of the subgenus. The phylogenetic relationships with allied species are, however, put off, at present, as a further problem.