Amussiopecten iitomiensis (Otuka, 1934)
OTUKA, Y. 1934. On some fossils from the Northern Foot of Mount Minobu and from Hayakawa Tuffite of Hakone (in Japanese). Journal of the Geological Society of Japan, 41 (492): 562-568. [p. 565, text-fig. 1]
Amussiopecten iitomiemis (Otuka); M. Akiyama,1957, Amussiopecten iitomiensis (Otuka) and its allies from Japan, plate 6, figures 1-6.
|
«This new species resembles Pecten naganumana YOKOYAMA, but the former has a flatter and higher shell than the latter. Patinopecten yessoensis JAY is allied to the present species, which has narrower and shallower interstices.
The measurements are as follows;
Ribs 14-15 in number.
The apical portion of this species is flat and resembles Pecten laqueatus SOWERBY. Ears are simple and triangular; byssal notch indistinct. Radial ribs rounded and become gradually flatter and obsolete towards the ventral and the lateral margins. The interstices narrower than the ribs themselves.» YANOSUKE OTUKA, 1934
[Original description from Masahiko Akiyama, 1957] |
«Remarks. — This species is characterized by the rather thin, large shell which is provided with 11-15 rounded, straight. radial ribs. The ribs become obsolete at the ventral and the lateral margins, and are much broader than the interstices. The present species, as was pointed out by T. SHUTO (1955), has variable characters. Above all, theshell outline varies from opithocline to prothocline through orthocline and from .33 to .62 in lnequilarity.
Amussiopecten hyugaensis SHUTO is synonymous with this species. A. praesignis (YOKOYAMA) is closely allied to the present species, but the latter has less numerous, rounded, radial ribs which never split into riblets and the interstices are much narrower. A. planicostulatum (NOMURA and NIINO) is also allied to the present species, but the latter has less numerous ribs which never split into riblets. Geological significance: — T. SHUTO has stated that "A. hyugaensis" occurs from the lower part of the Miyazaki group in south-east Kyushu, while A. praesignis is found from the upper horizon of the Takanabe member. Considering the above mentioned facts and the morphological relationship of these two species, it may be suggested that A. praesignis is derived from A. iitomiensis (A. hyugaensis). If this is true, the Shizukawa sandstone (OTUKA 1955) in Yamanashi Prefecture which yields A. iitomiemis may be Upper Miocene in age. Unfortunately, the writer has had no chance to examine A. praesignis (?) reported from the Sagara formation, but in the future, he wishes to collect and study those specimens and to clarify the phylogenetic relationship between A. praesignis and A. iitomiensis.» AKIYAMA, M. 1957. Amussiopecten iitomiensis (Otuka) and its allies from Japan. Transactions and Proceedings of the Palaeontological Society of Japan [N. S.], 25: 31-39, pls. 6-7, text-figs. 1-2. [p. 37, 38]
|
Amussiopecten iitomiemis (Otuka); M. Akiyama,1957, Amussiopecten iitomiensis (Otuka) and its allies from Japan, plate 7, figure 1.
|