. Bulletins of American paleontology. 50 Bulletin 331 holotype (PI. 4. fig. 13). a few indi\iduals from locality Nagasaki 3, Nagasaki Prefecture, clearly show a faint trans\erse callus groo\e or depression (PI. 4, figs. 14b. 15b). This feature is considered to be an intraspecific Nariation of ,V. eocenica. .\ similar variation of the transverse groove has also been recorded in Neverita globosa Gabb, 1869, from the upper Paleocene to upper Eocene of western North .America by Givens and Kennedy (1976) and Marin- covich (1977). Marincovich (1977, p. 315) mentioned that "a few indi\ iduals of
. Bulletins of American paleontology. 50 Bulletin 331 holotype (PI. 4. fig. 13). a few indi\iduals from locality Nagasaki 3, Nagasaki Prefecture, clearly show a faint trans\erse callus groo\e or depression (PI. 4, figs. 14b. 15b). This feature is considered to be an intraspecific Nariation of ,V. eocenica. .\ similar variation of the transverse groove has also been recorded in Neverita globosa Gabb, 1869, from the upper Paleocene to upper Eocene of western North .America by Givens and Kennedy (1976) and Marin- covich (1977). Marincovich (1977, p. 315) mentioned that "a few indi\ iduals of A\ (N.) globosa show a faint transverse callus groove when examined in strong oblique light" (see Givens and Kennedy, 1976, pi. 2, figs. 7, 11, 14). Marincovich (1977) argued that A'. globosa may be the ancestral stock from which Gloss- aiilax Pilsbry, 1929, evolved because of the following three reasons: (1) the incipient development of the um- bilical callus groove of N. globosa is interpreted as a forerunner of Glossaulax, which is characterized by presence of the distinct umbilical callus groove; (2) the stratigraphic distribution of A", globosa (upper Paleo- cene to upper Eocene) partly overlaps that of the ear- liest known species of Glossaulax, G. rechisiana (Des- hayes, 1839) (middle Eocene to Holocene); and (3) TV. globosa and G. rechisiana lived in the same region at the same time (western North America during the mid- dle to late Eocene). I consider N. eocenica to be very closely related to A^. globosa, and to be a member of the ancestral stock of Glossaulax. However, A^. eocenica might not be the direct ancestor of species of Glossaulax in Japan. In the northwestern Pacific, Glossaulax first appeared in the early middle Miocene [Glossaulax didyma coti- cazae (Makiyama, 1926)], and there is a wide strati- graphic gap between N. eocenica and G. didyma coti- cazae. The ancestor of species of Glossaulax in Japan, therefore, is thought to be G. rechisiana, the
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