The California lucine, Epilucina californica (Conrad, 1837), is reported from lower Middle Miocene to Upper Pliocene strata in Japan. This extends the oldest record of this species and represents the first detailed record of the species and genus in the western North Pacific region. Based on the Paleogene fossil record of Epilucina and the general migration pattern of Neogene North Pacific mollusks, it is inferred that E. californica originated in the eastern North Pacific during Late Oligocene or Early Miocene time and migrated westward to the western North Pacific during the early Middle Miocene. The western North Pacific populations of E. californica became extinct by the end of the Pliocene, whereas the eastern North Pacific populations survive in California. This species is, therefore, regarded as a northeastern Pacific restriction taxon. Two Japanese fossil species, Lucina (Myrtea) nipponica Nomura and Hatai, 1936 and Lucina japonica Ozaki, 1958 are junior synonyms of E. californica.
Introduction
Both the Asian and American sides of the middle latitude North Pacific have a fairly well-documented Cenozoic marine fossil record which provides data for examining historical marine biogeography. Since the publication of Vermeij's (1989) general survey of geographical restriction of cool-temperate faunas during the Neogene, our knowledge of the Neogene trans-Pacific interrelationship between western and eastern North Pacific mollusks has steadily accumulated (e.g., Vermeij, 1991, 2001; Amano et al., 1993, 1999; Amano, 1998, 2005; Amano and Vermeij, 1998, 2003; Amano and Hikida, 1999; Matsubara, 1994, 2003; Reid, 1996; Nakashima, 1999).
This paper focuses on the lucinid bivalve genus Epilucina Dall, 1901. This genus is restricted today to the warm-temperate Californian Province, and is represented there by the single species Epilucina californica (Conrad, 1837), the type species of the genus (Coan et al., 2000). The fossil record of Epilucina has been predominantly reported from the Pacific side of North America and Central America, and the oldest record goes back to the Upper Eocene (Squires and Gring, 1996).
The fossil occurrence of E. californica in Japan was briefly presented by Kurihara and Nakashima (2003). Recently, Nemoto and O'Hara (2005) illustrated E. californica from the Pliocene of northeast Japan. This paper provides the first detailed documentation of E. californica from the Neogene of Japan and also discusses the biogeographic history of Epilucina.
Abbreviations used for catalog numbers are: LACM, Natural History Museum of Los Angeles County, California, U.S.A.; MFM, Mizunami Fossil Museum, Mizunami, Japan; NSMT, National Science Museum, Tokyo, Japan; SHM, Saito Ho-on Kai Museum of Natural History, Sendai, Japan.
Material and methods
Stratigraphic distribution and ages
Fossil and Recent specimens of Epilucina californica (Conrad) examined in this study are summarized below. All Japanese localities where I have examined fossil specimens are shown in Figure 1 (see also Appendix). The following stratigraphic units are listed from the oldest to the youngest geological age.
Nataki Member of Oidawara Formation, Mizunami Group.—The Nataki Member is the basal unit of the Miocene Oidawara Formation, the Mizunami Group, distributed in the Mizunami area, Gifu Prefecture, central Honshu. This member consists mainly of sandstone and conglomerate and yields warm-water marine mollusks. Itoigawa in Itoigawa et al. (1974) described a pair of well-preserved valves (MFM 11245) of E. californica under the name of Notomyrtea minoensis Itoigawa, 1960 from the conglomerate of the Nataki Member (loc. Mizunami in Figure 1 and Appendix). Thereafter, Itoigawa et al. (1981, 1982) reidentified the same specimen as Codakia? sp. The geologic age of the Oidawara Formation is well documented as the early Middle Miocene by microfossil biostratigraphy (e.g., Saito, 1963; Yanagisawa, 1993).
Kubota Formation.—The Kubota Formation [= Tanagura shell beds] is a fossiliferous marine deposit exposed in the Tanagura area, Fukushima Prefecture, northeast Honshu. Nomura and Hatai (1936) described a single left valve (SHM 6902) of E. californica under the name of Lucina (Myrtea) nipponica Nomura and Hatai, 1936 from this formation (loc. Tanagura in Figure 1 and Appendix). They reported 22 molluscan taxa indicative of open-marine environments from the same locality. The stratigraphic horizon of the fossil locality is in the upper part of this formation. The geologic age of the whole Kubota Formation is well assigned to the early Late Miocene by fission track and K-Ar datings (Takahashi et al., 2001a, b) and by microfossil biostratigraphy (Shimamoto et al., 1998; Hayashi et al., 2002; Yanagisawa et al., 2003).
Naarai Formation.—The Naarai Formation consists of 150-m-thick marine deposits exposed on the Choshi Peninsula, Chiba Prefecture, central Honshu. This formation has a basal conglomerate yielding abundant marine fossils (e.g., Ozaki, 1954a, 1954be.g., Ozaki, 1958; Oishi and Hasegawa, 1994). Ozaki (1958) described a single well preserved left valve (NSMT 4422) of E. californica under the name of Lucina japonica Ozaki, 1958 from the basal conglomerate (loc. Choshi in Figure 1 and Appendix). According to T. Sato in Oishi and Hasegawa (1994), the basal conglomerate of the Naarai Formation contains calcareous nannofossils indicative of the Lower Pliocene.
Dainenji Formation of Sendai Group.—The Dainenji Formation is the uppermost unit of the Sendai Group, distributed widely in the coastal areas in Miyagi and Fukushima Prefectures, northeast Honshu. According to Kubo et al. (1994), this formation in the Iwaki-Tomioka area is composed mainly of marine sandstone and diatomaceous mudstone, and is divided into five lithofacies (D1a, D1b, D1c, D2 and D4 in ascending order). At loc. Iwaki-Tomioka in Figure 1 and Appendix, the D4 facies contains a sequence of submarine slide deposits, which consist of a slide block (3–4 meter thick), pebbly very coarse- to coarse-grained sandstone containing abundant molluscan fossils (4 meters thick), and bedded medium-grained sandstone (1 meter thick), in ascending order (Kohno and Yanagisawa, 1997). This molluscan assemblage is characterized by a mixture of shallow-and deep-water forms (Nemoto and O'Hara, 2005). Shell fragmentation and signs of wear are commonly observed in the shallow-water mollusks, which contain both warm- and cold-water inhabitants. A single well preserved right valve (NSMT PM14857) and some small fragmental valves of E. californica were collected from this assemblage. The geologic age of the fossiliferous horizon is well determined as the Late Pliocene by diatom biostratigraphy (Kohno and Yanagisawa, 1997)
“San Pedro Formation”.—Three isolated valves of E. californica with an old label written as “Pliocene, Saugus, San Pedro, California” (SHM 13177, 13200) were examined. The stratigraphic horizon they were collected from is not clearly indicated on the label, but they are probably from the San Pedro Formation, which is one of the classic fossiliferous marine sequences distributed mainly in the coastal areas of Los Angeles County, California. This formation is mostly Pleistocene in age, but the lower part extends to the Upper Pliocene (Powell and Stevens, 2000). In this study, the present specimens are treated as from the Plio-Pleistocene “San Pedro Formation”.
Recent.—Twenty-three shells of E. californica (LACM 168194) from White's Pt., Los Angeles County, California were examined.
Measurements
I measured the shell length (L), shell height (H), shell width (W ) and number of commarginal ribs (Nc). Method of the number of commarginals follows that of Shuto (1971). The commarginals are counted at a unit distance on the line connecting the umbo to the middle part of the ventral margin and expressed in the formula of, for example, 14/5 (5–10), which means that the commarginals are 14 per 5 mm between 5 and 10 mm from the ventral margin on the measured line.
Systematic descriptions
Family Lucinidae Fleming, 1828
Subfamily Lucininae Fleming, 1828
Genus Epilucina Dall, 1901
Type species.—Lucina californica Conrad, 1837, by original designation, Miocene to Recent, California and Japan.
Emended diagnosis.—Shell medium to large, subcircular, longer than high, moderately inflated. Anterior expansion moderate, posterior shell margin often truncate. Sculpture of closely spaced commarginal ribs with irregularly spaced growth lines. Posterior dorsal area distinct. Lunule medium in size, lanceolate, strongly asymmetric. Ligament external, long. Anterior adductor scar long, narrow, generally curved, diverging from pallial line. Anterior and posterior laterals single in right valve, double or socket-like in left; two cardinals in each valve. Inner ventral margin almost smooth.
Discussion.—The most remarkable features of this genus are the closely spaced commarginal ribs, the absence of remarkable radial ornaments, the distinctly asymmetric lunule, and the strong anterior and posterior lateral teeth in both valves. Until recently, Epilucina had been treated as a subgenus of such genera as Codakia, Myrtea and Lucina (see species synonymy). Table 1 shows the summary of shell characters of Epilucina, Codakia, Myrtea and Lucina. Epilucina is clearly distinguishable from the latter three genera by a combination of these shell characters (e.g., shell sculpture, marginal crenulae, lunule, ligament, and hinge plate and teeth). Therefore, I recognize Epilucina as an independent genus, as do also Coan et al. (2000).
Table 1.
Summary of shell characters of Epilucina, Codakia, Myrtea and Lucina.
Included species.—Fossil and Recent mollusks that are safely or certainly assignable to this genus besides the type species are: Corbis washingtoniana Clark, 1925 from the Upper Eocene of California and Oregon, North America, Lucina (Epilucina) gabrielensis Clark, 1946 from the Upper Eocene of Colombia, South America and Lucina (Epilucina) zapotalensis Olsson, 1931 from the Middle Oligocene of Ecuador, South America (Squires and Gring, 1996). Some European paleontologists have assigned Lucina haidingeri Hörnes, a European Tertiary lucinid, to Epilucina (e.g., Schultz, 2003, p. 386–387). Although this species entirely lacks radial ornaments on the shell surface, it seems to be related to the genus Codakia rather than Epilucina because of their similarity in shell outline and hinge structure. C. haidingeri has a circular shell outline, a broad hinge plate and a weak and short posterior lateral tooth, and is excluded from Epilucina herein.
Epilucina californica (Conrad, 1837) Figures 2, 3; Table 2
Figure 2.
Recent specimens of Epilucina californica (Conrad, 1837). Loc. White's Pt., Los Angeles County, California, selected specimens from LACM 168194. 1a–c. Interior and exterior of right valve and dorsal view of articulated valves, a, ×3.0; b, c, ×2.0. White line drawing indicates the outline of muscle scars. aa, anterior adductor muscle scar; ap, anterior pedal retractor muscle scar; pa, posterior adductor muscle scar; pb, pallial blood vessel scar. 2a, b. Exterior of right valve and dorsal view of articulated valves, ×2.0. 3a–d. Details of hinge of right and left valves, exterior of left valve, and dorsal view of articulated valves, a, b, ×2.4; c, d, ×1.5.
Figure 3.
Fossil specimens of Epilucina californica (Conrad, 1837) from Japan and California. All the specimens ×1.2 otherwise stated. 1a–c. Exterior and interior of right valve and dorsal view of articulated valves, MFM 11245, loc. Mizunami, lower Middle Miocene Nataki Member of Oidawara Formation. 2a–c. Exterior, interior and dorsal view of left valve, SHM 6902, holotype of Lucina (Myrtea) nipponica Nomura and Hatai, 1936, loc. Tanagura, lower Upper Miocene Kubota Formation, ×1.7. 3a–c. Exterior, interior and dorsal view of left valve, NSMT 4422, holotype of Lucinia japonica Ozaki, 1958, loc. Choshi, Lower Pliocene Na-arai Formation. 4a–c. Exterior, interior and dorsal view of right valve, NSMT PM14857, interior and dorsal view of left valve loc. Iwaki-Tomioka, Upper Pliocene Dai-nenji Formation. 5. Exterior of left valve, SHM 13177, loc. Saugus, San Pedro, Californica, Plio-Pleistocene “San Pedro Formation”.
Table 2.
Measurements of fossil Epilucina californica (Conrad). *1 = holotype of Lucina japonica Ozaki; *2 = holotype of Lucina (Myrtea) nipponica Nomura and Hatai.
L[ucina] californica Conrad, 1837, p. 225, pl. 20, fig. 1.
Lucina (Myrtea) californica Conrad. Grant and Gale, 1931, p. 285–286, pl. 14, figs. 15a, b, 21a, b.
Lucina (Epilucina) californica Conrad. Hertlein and Grant, 1972, p. 247–248, pl. 46, figs. 11, 16.
Myrtea? (Epilucina) californica (Conrad). Bretsky, 1976, p. 301, pl. 35, figs. 1–3.
Codakia (Epilucina) californica (Conrad). Moore, 1988, p. D11–D12, pl. 1, figs. 16, 17.
Epilucina californica (Conrad). Coan et al., 2000, p. 263, pl. 50; Nemoto and O'Hara, 2005, pl. 8, figs. 1a, b.
Lucina (Myrtea) nipponica Nomura and Hatai, 1936, p. 123–124, pl. 15, figs. 12a, b.
Lucina japonica Ozaki, 1958, p. 126, pl. 10, figs. 11, 12.
Notomyrtea minoensis Itoigawa. Itoigawa in Itoigawa et al., 1974, p. 79, pl. 20, figs. 1a, b (non Notomyrtea minoensis Itoigawa, 1960).
Codakia? sp. Itoigawa et al., 1981, pl. 12, figs. 15a, b; Itoigawa et al., 1982, p. 61.
Types.—
Lucina californica Conrad: type material unknown (Hertlein and Grant, 1972); type locality, muddy marshes near San. Diego, San Diego County, California, Recent.
Lucina (Myrtea) nipponica Nomura and Hatai, 1936: SHM 6902 (holotype: Figures 3.2a–c), from Okada, Tanaguramachi, Higashi-Shirakawagun, Fukushima Prefecture, lower Upper Miocene Kubota Formation.
Lucina japonica Ozaki, 1958: NSMT 4422 (holotype: Figures 3.3a–c), from Cape Inuwaka, Choshi City, Chiba Prefecture, Lower Pliocene Na-arai Formation.
Description.—Shell medium in size, H rarely exceeding 40 mm, slightly to distinctly longer than high (H/L range 0.876–0.974), weakly to moderately inflated (W/L range 0.183–0.285), white, solid. Anterior margin well rounded, posterior margin widely rounded to subtruncated. Umbones small. Sculpture of low, closely spaced, rounded to somewhat angulated, irregular commarginal ribs; Nc range 10–19/5 (5–10) (L < 25 mm) and 8–14/5 (5–10) (L > 25 mm); faint radial striations sometimes visible microscopically. Wide posterior dorsal area demarcated by a sulcus which runs from the umbo to the posterior shell margin. Anterior dorsal area not defined. Lunule small, lanceolate, finely ribbed, strongly asymmetric, greater part lying in right and fitting into concave depression in left valve. Ligament external, long and set in shallow groove. Hinge in right valve has two cardinal teeth, anterior tooth is smaller than the posterior one and mostly sunken in the lunule; anterior and posterior lateral teeth prominent, anterior teeth stronger than posterior teeth. Left valve with two cardinal teeth, anterior tooth slender and posterior one prominent; anterior and posterior lateral teeth and sockets prominent, anterior teeth stronger than posterior teeth. Anterior adductor muscle scar long, narrow, detached from pallial line for about 70% of length. Anterior pedal retractor muscle scar separate from the adductor. Posterior adductor muscle scar small, sub-circular. Pallial line narrow, entire. Pallial blood vessel scar present. Shell margin smooth or radially striate, not crenulate.
Discussion.—In the fossil specimens examined, the hinge plate is mostly incomplete. Especially the posterior lateral teeth and socket tend to be broken (e.g., Figures 3.3b, 3.4b). Two Japanese fossil species, Lucina (Myrtea) nipponica Nomura and Hatai, 1936 and Lucina japonica Ozaki, 1958 and one unnamed species Codakia? sp. of Itoigawa et al. (1981, 1982) (= Notomyrtea minoensis Itoigawa of Itoigawa et al., 1974) are presently regarded as junior synonyms of Epilucina californica herein. According to Nomura and Hatai (1936) describe, L. nipponica as “resembling closely L[ucina] californica Conrad from the Californian waters in general aspects, but differing in possessing a smaller shell, finer sculpture and with a somewhat different outline”. Ozaki (1958) stated that “the present new species [L. japonica] differs from the latter [L. californica] in having a more pointed beak, more numerous and finer concentric riblets and a roundly protruded anterodorsal margin”. However, these slight differences are not sufficient criteria for separating them from Epilucina californica. As shown in Figure 2, the shell outline of E. californica is considerably variable in the Holocene population (Coan et al., 2000). Bretsky (1976) noted for E. californica that the shell is medium size (median L of 18 specimens 27 mm, range 12–38 mm) and slightly to distinctly longer than high (median H/L 0.93, range 0.86–0.97). My observation on the relationships between L and H/L and W/L of the Plio-Pleistocene and Recent specimens of E. californica also indicate wide variations within which the Japanese fossil specimens are included (Figure 4). Nc and the thickness of the hinge plate are also considerably variable in the Recent specimens. Examination of the type specimens of Lucina nipponica, L. japonica and Codakia? sp. and the Plio-Pleistocene and Recent specimens of E. californica from California reveals that these Japanese and American species cannot be separated by shell shape and sculpture.
Figure 4.
Relationship between H/L (triangle) and W/L (square) ratios and L of fossil and Recent Epilucina californica. *1 = holotype of Lucina japonica Ozaki.
Epilucina washingtoniana (Clark, 1925, p. 90, pl. 20, figs. 1–4) from the Upper Eocene of the Pacific side of North America differs from this species in its larger shell (L 3–6 cm: Squires and Gring, 1996) with coarser commarginal ribs. Epilucina gabrielensis (Clark, 1946, p. 60, pl. 12, fig. 6) from the Upper Eocene of Colum bia is distinguished from this species in its larger shell (L 54.4 mm, H 54.4 mm in holotype: Clark, 1946) with finer commarginal ribs. Epilucina zapotalensis (Olsson, 1931, p. 49, pl. 5, figs. 2, 5) from the Middle Oligocene Mambri shales near Zopotal, Ecuador resembles this species except for its large shell size (attaining 47 mm in length, 43 mm in height), but a detailed comparison cannot be made due to the poor preservation of E. zapotalensis.
Occurrence in Japan.—Lower Middle Miocene to Upper Pliocene. Lower Middle Miocene: Nataki Member of Oidawara Formation, Mizunami Group, Gifu Prefecture, central Honshu; Lower Upper Miocene: Kubota Formation, Fukushima Prefecture, northeast Honshu; Lower Pliocene: Na-arai Formation, Chiba Prefecture, central Honshu; Upper Plio-cene: Dainenji Formation of the Sendai Group, Fu-kushima Prefecture, northeast Honshu. This species is extremely rare, and is represented only by a single or a few specimens from one locality in each formation. Kurihara and Nakashima (2003) recorded the occurrence of poorly preserved specimens of Epilucina species from the Pliocene Komahata Formation of Hokkaido. However, later examination revealed that the Komahata specimens should be identified as a venerid (probably Phacosoma or Kaneharaia) rather than a lucinid. Therefore, the occurrence of Epilucina from the Pliocene of Hokkaido is excluded herein.
Occurrence in North America.—Moore (1988, p. D11–D12) gave the fossil occurrence of E. californica as from the Miocene to the Pleistocene in California. The oldest record of this species in North America is from the Upper Miocene Santa Margarita Formation (Preston, 1931). Modern distribution: Crescent City, California (41.8°N) to Rocas Alijos, Baja California Sur (25.0°N), in the low intertidal zone to 80 m, in sand and gravel of exposed foreshores (Coan et al., 2000).
Biogeographic history of Epilucina
Figure 5 shows the stratigraphic ranges of Epilucina species with inferred paleobiogeographic events. The fossil record indicates that Epilucina appeared in the Eastern Pacific region during the Late Eocene. The earliest members safely assignable to the genus Epilucina in having the characteristic asymmetric lunule are Epilucina washingtoniana (Clark, 1925) from Washington and California, North America and Epilucina gabrielensis (Clark, 1946) from Columbia, South America, both Late Eocene species (Squires and Gring, 1996). The former species is regarded as a chemosynthetic bivalve because it occurs abundantly in cold-seep associated fauna, whereas the latter species is a non-chemosynthetic one found in shallow-marine molluscan assemblages (Squires and Gring, 1996). Epilucina zapotalensis (Olsson, 1931), whose lunule cannot be observed due to poor preservation, is the sole Oligocene species of the genus and is a possible ancestor of E. californica. There is no published record of Epilucina in the Paleogene of the western North Pacific region (i.e., Japan and Russian Far East).
Figure 5.
Stratigraphic ranges of Epilucina species with inferred paleobiogeographic events. For stratigraphic ranges, heavy solid lines are based on reliable fossil record; heavy dashed lines show inferred missing occurrences. See text for details.
During the Neogene and Quaternary, Epilucina is represented only by a single species, E. californica. This species appears to have had a disjunct geographic distribution in the eastern and western North Pacific during the Neogene. On the Pacific side of North America, this species has been recorded in California from the Upper Miocene to Recent. In Japan, as discussed above, this species ranges from the lower Middle Miocene to the Upper Pliocene.
It is inferred that E. californica originated in the eastern Pacific from a stock of Paleogene Epilucina, and that this species migrated westward to the western North Pacific during early Middle Miocene time. This is based largely on the geographic distribution of the Paleogene fossil record of Epilucina mentioned above and on the general migration pattern of the Neogene amphi-North Pacific taxa. Many marine molluscan clades with an Oligocene to Early Miocene origin in North America expanded westward in the North Pacific and reached temperate coasts of Japan by the early Middle Miocene (see Vermeij, 2001; Amano, 2005). They contain such genera as Littorina (Reid, 1996), Glossaulax, Cryptonatica (Marincovich, 1977; Majima, 1989), Liracassis (Kanno, 1973; Moore, 1984), Nucella (Amano et al., 1993), Ceratostoma (Amano and Vermeij, 1998), Lirabuccinum (Vermeij, 1991; Amano and Vermeij, 2003), and Rexithaerus (Matsubara, 1994; Amano et al., 1999). Their first stratigraphic occurrence in Japan is Early or early Middle Miocene in age, as is also the case for E. californica. The expansion apparently coincided with the Mid-Neogene Climatic Optimum (MNCO) or an episode of maximal Neogene warmth in the North Pacific, when relatively warm-water molluscan genera reached the Gulf of Alaska (Marincovich and Kase, 1986; Marincovich, 1988; Marincovich and Moriya, 1992) and the Sea of Okhotsk (Amano et al., 1996). The northward expansion of the temperate zone in the North Pacific due to the MNCO probably enabled Epilucina to migrate to the western North Pacific. On the other hand, another possible hypothesis on the history of E. californica proposes a western North Pacific origin and an eastward migration. This is largely based on the chronological difference of its apparent first stratigraphic occurrence between Japan and California, and supposes that Epilucina migrated during the late Paleogene from the eastern Pacific to Japan, and that E. californica migrated from Japan to California during the Middle or Late Miocene. Thus, this hypothesis requires trans-Pacific (westward and eastward) migration two times during the late Paleogene and middle Neogene, which seems less plausible than the former hypothesis with its eastern North Pacific origin and only a single trans-Pacific (westward) migration. The lack of the fossil record of E. californica from Lower and Middle Miocene strata on the Pacific side of North America can be explained by its extremely rare fossil occurrence, as in Japan.
In the Quaternary of Japan, there is no reported occurrence of E. californica in spite of the presence of many fossiliferous localities yielding Quaternary shallow marine mollusks. This strongly suggests that the western North Pacific populations of E. californica might have become extinct by the end of the Pliocene. Using Vermeij's (1989) categories, the paleobiogeo-graphic pattern of E. californica is “the northeastern Pacific restriction”, in which species with a previously amphi-Pacific distribution have become restricted to the American side. Vermeij (1989) showed that the northeastern Pacific restriction taxa are much fewer than the northwestern Pacific restriction taxa, in which species with a previously amphi-Pacific distribution have become restricted to the Asian side. Amano (1998) pointed out that the venerid bivalve Humilaria shows a northeastern Pacific restriction and a short-term invasion from western North America to Japan. He also briefly reviewed the following clades as showing northeastern Pacific restriction during the Neo-gene: the venerid bivalve Compsomyax, the myid bivalve Platyodon, and the murcid gastropod Nucella shiwa (Chinzei). The last stratigraphic occurrences of these clades in Japan are the end of the late Early Miocene (Platyodon), the end of the early Middle Miocene (Compsomyax), and the end of the Early Pliocene (Humilaria and Nuccella shiwa). This inconstancy of last occurrences indicates that the northeastern Pacific restriction cannot be triggered by a synchronous event. Amano (1998) suggested the success of ecologically similar species as the reason for the regional extinction of Humilaria in Japan. In the case of E. californica, however, there is no ecologically comparable species in the modern intertidal and sublittoral fauna of warm-temperate Japan, and the reason why only the western North Pacific populations became extinct is unknown.
Acknowledgments
I am grateful to Rei Nakashima (Geological Survey of Japan) for discussion, and to Joseph G. Carter (University of North Carolina at Chapel Hill) for critically reading the early draft of the manuscript. Sadako Takeuti (SHM), Tomoki Kase (NSMT), Yoshitsugu Okumura and Hiroaki Karasawa (MFM), and Lindsey L. Groves (LACM) arranged for the loan of type and comparative specimens in their care. Pierre Lozouet (Muse ′um National d'Histoire Naturelle, Paris) allowed me to examine specimens of Lucina haidingeri in his fossil mollusk collection from the Aquitaine Basin, and Ortwin Schultz (Naturhistorisches Museum Wien) provided me some information on L. haidingeri. I would like to thank the reviewers, Kazutaka Amano and Geerat J. Vermeij, for their constructive comments that helped to improve the manuscript.
References
Appendices
Appendix
Localities cited
Collecting localities of Epilucina species from the Neogene formations in Japan (Figure 1) are alphabetically listed below.
Choshi [35° 51′ 46″N; 140° 50′ 47″E]; calcareous sandstone exposed during the construction of Inuwaka Fishery Port at Cape Inuwaka, Tyôsi [Choshi] City, Chiba Prefecture, central Honshu, Japan. Basal conglomerate of the Na-arai Formation. Age: Lower Pliocene. Collector: H. Ozaki, date unknown.
Mizunami [exact latitude and longitude unknown]; Dan, Tokicho, Mizunami City, Gifu Prefecture, central Honshu, Japan. Nataki Member of the Oidawara Formation. Age: lower Middle Miocene. Collector & date: unknown. [= Loc. N (64) of Itoigawa et al., 1981, 1982].
Iwaki-Tomioka [42° 42′ 40″N, 143° 19′ 6″E]; Pebbly very coarse- to coarse-grained sandstone exposed at beach cliff, about 500 m N of Oragahama Fishery Port, Tomiokamachi, Fukushima Prefecture, northern Honshu, Japan. Dainenji Formation. Age: Upper Pliocene. Collector: Y. Kurihara, date: 1998–1999. [= locality of NSM PV-20072 of Kohno and Yanagisawa, 1997].
Tanagura [37°01′N, 140°26′03″E]; Coarse-grained sandstone cropping out at cliff bordering stream immediately NW of Okada, Yamaokamura [Tanaguramachi], Higashi-Shirakawa gun, Fu-kushima Prefecture, northern Honshu, Japan; upper part of the Kubota Formation; lower Upper Miocene. Collector: Tsunoda, date unknown. [= loc. Okada of Nomura and Hatai, 1936].
