Abstract
In 1937, one of the present writers (OINOMIKAD0) made a large collection offossil shells from the Usigakubi bed of the Higasiyama Oil Field, Niigata-ken. Some specimens of a peculiar shaped vivalve, Calyptogena nipponica n. sp. have been founded among the fossil fauna. In the same year, the another writer (KANEHARA) visited the oil field, and obtained two specimens of this new species from a water well sunk into the black shale of the Kubiki series at Nakanosawa, Higasiyama-mura, Niigata-ken.
There are three known species of the genus Calyptogena, including C. nipponica, which seems to be extinct. C. pacifica DALL is living in the Clarence Strait, Alaska to the Santa Barbara Channel, California, and is also known as a fossil from the Pliocene of California. Recently it was reported by OTUKA from the Pliocene of the Oga Peninsula, Akita-ken, Japan. C. elongata DALL is another representative of the genus, and now living in the waters of Santa Barbara Islands to San Diego, California.
The specimens from the Usigakubi bed were contributed to the Imperial Geological Survey of Japan from the Nippon Oil Company.
