Along the Wakamatsukita Coast and the coastlines of Ainoshima Island and Umashima Island of Kitakyushu City, geographical strata called the Ashiya Group can be seen. In these layers, fossils of Glycymeris albolineata are what remain of the bivalve clams thought to have inhabited the warm sea. Glycymeris cisshuensis, which are related to the Glycymeris vestita, are excavated here in a concentrated manner.