. Bulletins of American paleontology. Japanese Cenozoic Naticids: Majima 19 Miyagi Prefecture (PI. 5, figs. 20-25, PI. 6, figs. 1-2), Shigarami 1, Nagano Prefecture (PI. 6, fig. 3), and the Nodani Formation, Joetsu City, Niigata Prefecture (Amano, Kanno, and Mizuno, 1985, pi. 2, fig. 14) are assigned to G. didyma coticazae. They show the glo- bose to elongate form and deeply incised umbilical callus groove of G. didyiua coticazae but some speci- mens also possess the greatly developed umbilical cal- lus that characterizes one end form of 6". didyma di- dyma (Text-fig. ). Thus these ass
. Bulletins of American paleontology. Japanese Cenozoic Naticids: Majima 19 Miyagi Prefecture (PI. 5, figs. 20-25, PI. 6, figs. 1-2), Shigarami 1, Nagano Prefecture (PI. 6, fig. 3), and the Nodani Formation, Joetsu City, Niigata Prefecture (Amano, Kanno, and Mizuno, 1985, pi. 2, fig. 14) are assigned to G. didyma coticazae. They show the glo- bose to elongate form and deeply incised umbilical callus groove of G. didyiua coticazae but some speci- mens also possess the greatly developed umbilical cal- lus that characterizes one end form of 6". didyma di- dyma (Text-fig. ). Thus these assignments are somewhat arbitrary. The other Pliocene populations studied herein are morphologically closer to G. didyma didyma and are assigned to this subspecies. Glossaulax didyma dainichiensis. n. subsp. is a late Pliocene geographic subspecies of the G. didyma co- ticazae - G. didyma didyma lineage. It is restricted geographically to the Kakegawa area on the Pacific side of central Honshu (Shizuoka Prefecture), and strati- graphically to a narrow horizon: lower part of the upper Pliocene Dainichi Member of the Lower Kakegawa Formation. This limited occurrence suggests that G. didyma dainichiensis was a local subspecies in the late Pliocene. Glossaulax didyma dainichiensis shows a very wide range of morphology (PI. 7, figs. 6-16), including some characteristics of both G. didyma coticazae (a deeply incised umbilical callus groove: PI. 7, figs. 14- 16) and G. didyma didyma [both the end forms of the umbilical callus: a small subtrigonal umbilical callus detached from the posterior side of the umbilicus (PI. 7, figs. 10-11), and a greatly developed umbilical callus largely covering the umbilicus (PI. 7, figs. 6-7)]. Gloss- aulax didyma dainichiensis also includes one variant with a greatly depressed shell (PI. 7. figs. 13-15), and its transverse callus groove crosses obtusely to the in- ner margin of the aperture (Text-fig. 9 [angle A]). These characteristics are never observab
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