895. GIGANTIC AMMONITES FROM THE CRETACEOUS FUTABA GROUP OF FUKUSHIMA PREFECTURE

Abstract

Ten large or gigantic ammonite specimens were obtained by a number of persons from the Upper Cretaceous Futaba Group in the coastal area of Fukushima Prefecture (Northeast Japan). They are more or less incompletely preserved, but complementary with one another in showing characteristic features, which allow us to conclude that they are macroconchs of Mesopuzosia yubarensis (Jimbo). They can supplement in some respects the knowledge of this species, which has been recently described on the material from Hokkaido. They occur sporadically in a limited part (silty fine-grained sandstone and sandy mudstone) of the Coniacian Ashizawa Formation, i.e. the lower unit of the tripartite Futaba Group. For some reasons no microconch of this species has been found from the same part.