Vesicomya ( Calyptogena ) Peckmann et al. 2002: 861 Vesicomya ( Calyptogena ) Pleurophopsis chitanii ( Kanehara, 1937 ) P. thieli P. chitanii P. thieli P. chitanii P. chitanii P. thieli P. chitanii P. thieli P . chitanii P . chitanii Calyptogena Pleurophopsis Hubertschenckia Pleurophopsis thieli P. chinookensis P. chinookensis P. unioides P. thieli New taxa, records, and data for vesicomyid bivalves from Cenozoic strata of the North Pacific region Kiel, Steffen Amano, Kazutaka Goedert, James L. Acta Palaeontologica Polonica 2023 2023-06-21 68 2 297 320 C5TR7 Kiel & Amano & Goedert, 2023 Kiel & Amano & Goedert 2023 [151,409,1582,1611] Bivalvia Vesicomyidae Pleurophopsis Animalia Venerida 14 311 Mollusca species thieli sp. nov.   Figs. 11, 12.   2002  Vesicomya( Calyptogena)sp.;  Peckmann et al. 2002: 861, fig. 3C. 2003  Vesicomya( Calyptogena)sp.; Goedert et al. 2003: pl. 42: 6, 7.  Zoobank LCID: urn:lsid:zoobank.org:act: C3DAEBBE-2844-4BDB- BEA4-3C1C01A76A69.   Etymology: In honor of Bruce Thiel ( Portland, Oregon), in recognition of his help with fieldwork related to this project.  Type material:  Holotype: articulated internal mold showing pallial line and muscle scars ( NRMMo 204761).  Paratypes: mostly internal molds ( NRM Mo204762–65, 204826) from  Jansen CreekMember; articulat- ed or semi-articulated specimens with shell material ( Mo204794–797) and internal molds ( Mo204798–802 from Whiskey Creekseep deposit. Upper Eoceneto lower Oligocene, Washington State, USA.    Typelocality: Shoreline exposures approximately  800 msoutheast of the mouth of Rasmussen Creek, Clallam County, Washington State, USA.    Typehorizon:  Jansen CreekMemberof the Makah Formation, lower Oligocene.  Material.—About 25 specimensand fragments from the Whiskey Creek site, Pysht Formation (NRM Mo 204794– 204802, UWBM 97305, 06). About 34 specimensfrom the Jansen Creek Member of the Makah Formation, including four from near Rasmussen Creek (NRM Mo 204761–64) and about 30 from near the mouth of Jansen Creek, many in butterfly preservation (NRM Mo 204765–68, 204828). Nine specimensfrom UWBM loc. B6702 (= SR 2 in Peckmann et al. 2002), Lincoln Creek Formation (NRM Mo 204826, 27). Upper Eocene to lower Oligocene, Washington State, USA. UWBM 97038 was previously reported as  Vesicomya( Calyptogena)sp. by Peckmann et al. (2002).  Diagnosis.—Shell average size for genus, inflation slight to moderate, posterior side tapering, often bent downward due to concave ventral margin; anterior adductor muscle scar bean or D-shaped; posterior adductor muscle scar rather small, displaced anteriorly, near posterodorsal margin; hinge with two strong, radiating teeth in right valve and three in left valve; subumbonal pit large and deep.  Description.—Shell elongate, up to 57.6 mm long; umbones anterior, at about 20% of total shell length; blunt, low ridge running from umbones to posterior margin; no lunular incision or escutcheon; anterior margin evenly to acutely rounded; anterior half of ventral margin straight, posterior half slightly concave, giving shell curved appearance; posterodorsal margin either straight and slightly tapering ( Fig. 11D), or anterior half straight and parallel to ventral margin, and posterior half more strongly inclined toward the ventral (Fig. 12E); posterior margin evenly rounded. Anterior adductor muscle scar bean to D-shaped with posterior edge, pallial line starting at its posteroventral corner, extending subparallel to ventral shell margin, and bending upward and anteriorly near the posterior shell margin, to merge into ventral margin of posterior adductor muscle scar; posterior adductor muscle scar positioned at about 30% of total shell length, relatively small, with broad trapezoid area including the pedal retractor scar to its anterior; hinge plate short and moderately broad, with two strong, radiating cardinal teeth in each valve; RV with short cardinal tooth 1 originating under umbo, running oblique to anterodorsal shell margin, cardinal tooth 3a reduced, 3b originating under umbo, short, running oblique to posterodorsal shell margin; LV with short, thin cardinal tooth 2a running subparallel to anterodorsal shell margin, 2b thick, triangular or bifid, directly under umbo, 4b very short and thin, or reduced; oval subumbonal pit present in each valve.  Dimensions.—See Table 8.  Remarks.—Most similar to  Pleurophopsis thieli sp. nov.  Fig. 11. The vesicomyid bivalve  Pleurophopsis thieli sp. nov., from the upper Eocene Whiskey Creek seep deposit in the Pysht Formation in western Washington State, USA. A. NRM Mo 204797, small articulated specimen, showing inflation; left valve (A 1) and dorsal (A 2) views. B. NRM Mo 204795, semi-articulated specimen; left valve (B 1) and right valve (B 2) views. C. NRM Mo 204796, small left valve, showing lack of lunular incision. D. NRM Mo 204794, LV showing shell outline. E. NRM Mo 204799, hinge area and anterior adductor muscle scar of LV. F. NRM Mo 204800, hinge plate of right valve. G. NRM Mo 204801, hinge plate and ligament nymph of RV. H. NRM Mo 204802, hinge plate and ligament nymph of LV. All specimens are paratypes.  Fig. 12. Thevesicomyid bivalve  Pleurophopsis thieli sp. nov., from lower Oligocene, western Washington State, USA.  Jansen CreekMember, Makah → Formation(A–C, G); “Big slide”,  Jansen CreekMember, Makah Formation(D–F); UWBMloc. B6702,  Lincoln CreekFormation(H). A. Paratype, NRMMo 204762, internal mold of articulated specimen, showing anterior adductor muscle scar (aams), inflation, and long ligament; left valve (A 1) and dorsal (A 2) views. B. Holotype, NRMMo 204761, internal mold of articulated specimen, showing muscle scars and pallial lin; dorsal view of posterior part (B 1) and right valve (B 2). C. Paratype, NRMMo 204764, internal mold of LV, showing anterior adductor muscle scar and course of anterior part of pallial line. D. Paratype, NRMMo 204768, RV with preserved shell material, showing external sculpture. E. Paratype, NRMMo 204765, RV with preserved shell material, showing external sculpture. F. Paratype, NRMMo 204828, block with numerous specimens in butterfly preservation. G. Paratype, NRMMo 204763, rubber cast of LV hinge area. H. Paratype, NRM Mo 204826, anterior part of RV showing hinge dentition. B and C not coated with ammonium chloride.  is  Pleurophopsis chitanii( Kanehara, 1937)from Lower to Middle Miocene strata in Japan( Kanehara 1937; Hirayama 1973; Amano and Jenkins 2007; Amano and Kiel 2011). The main difference is in the posterior adductor muscle scar, which is smaller and more anteriorly positioned in  P. thieli, whereas  P. chitaniihas a very large posterior adductor muscle scar in an almost terminal posterior position. Specimens resembling  P. thielihave been reported as  P. chitaniifrom presumably Lower to Middle Miocene strata on Kayak Island, Alaska( Kanno 1971). In our view, the identity and relation of the Kayak Island specimens to either  P. chitaniior  P. thieliare somewhat uncertain. The size and morphological range of the specimens sketched and illustrated by Kanno (1971)suggests that they perhaps belong to more than one species. One illustrated specimen Kanno 1971: pl. 7: 6) shows a pams that appears to be in a somewhat intermediate position between those seen in  P. chitaniiand  P. thieli. Confusingly, although Kanno (1971)lists  P. chitaniionly from USGS loc. M 1769 inthe upper part of the Yakataga Formation on Kayak Island, Plafker 1974) lists only one mollusk from that locality, a sareptid bivalve. Plafker (1974)does, however, list  P. chitaniifrom the upper and lower Yakataga Formation at four other localities on Kayak Island. Plaf ker (1974) lists  Calyptogena n. sp.? from five additional localities, one of which (USGS loc. 15861), approximately 1.8 km east of Cape St. Peter is apparently the same, or very near loc. M1769 according to the map. Additional collecting effort is needed to clarify how many species of  Pleurophopsis(or possibly other vesicomyid genera) are present in the strata on Kayak Island, including the upper and lower Katalla Formation because Plafker (1974)also recorded?  Hubertschenckiaand a “vesicomyacid” from those strata. We also do not at present know anything about the local detailed geologic context for each of the sites listed and mapped by Plafker (1974); much more could be learned if these are discreet ancient seep sites. According to Addicott (1976: 123), the age of the Yakataga Formation on Kayak Island is Early Miocene, whereas the exposures on the mainland are Middle Miocene.   Pleurophopsis thielidiffers from the late Eocene  P. chinookensisby having a lower shell, more curved outline, resulting from its often slightly concave ventral margin and its sloping posterodorsal margin, whereas  P. chinookensishas nearly straight and subparallel posterodorsal and posteroventral margins. The Middle Miocene typespecies  P. unioidesalso has straighter and subparallel posterodorsal and posteroventral margins compared to  P. thieli, and furthermore has larger and more round anterior and posterior adductor muscle scars ( Van Winkle 1919; Kiel 2007; Krylova et al. 2010).  Stratigraphic and geographic range.—Seep deposits within the Pysht and Makah formations, upper Eocene to lowermost Oligocene, western Washington State, USA. NRM 14 311 1 holotype NRM United States of America lower Oligocene Mo Upper Eocene 14 311 1 Washington paratype United States of America Clallam County 800 Rasmussen Creek 14 311 1 Washington holotype lower Oligocene Jansen Creek Member Makah Formation 14 311 1 holotype UWBM, NRM United States of America Lincoln Creek The Lincoln Creek Formation 15 312 7 Washington paratype