Hokkaidoconcha sp.

Kiel, Steffen, Campbell, Kathleen A., Elder, William P. & Little, Crispin T. S., 2008, Jurassic and Cretaceous gastropods from hydrocarbon seeps in forearc basin and accretionary prism settings, California, Acta Palaeontologica Polonica 53 (4), pp. 679-703 : 686-687

Hokkaidoconcha sp.

Fig. 5I .

Material.— Two specimens from NW Berryessa (site 10; figured specimen: UCMP 555094 ) .

Description.—Broad cerithioid shell with three or more whorls and deeply incised suture; whorls variably convex, sculptured by widely spaced and sometimes with very strongly opisthocyrt ribs, and broad, almost flat−topped spiral cords, nine such spirals per whorl; these cords are separated by narrow interspaces, numerous fine and opisthocyrt growth lines give spiral cords and their interspaces an undulating appearance; subsutural spiral is most strongly developed and also axial ribs are strongest near the suture, producing tubercles at their intersections; base appears to have only spiral ornament.

Discussion.—This species is listed here among Hokkaidoconcha solely because is shares the strong subsutural tuberculate cord with the Hokkaidoconcha species described above. But it differs markedly from them by having a broader apical angle, the whorls are more convex, the ribs are opisthocyrt rather than opisthocline, and the spiral cords are broad and flat−topped in contrast to the fine spiral threads of Hokkaidoconcha . Aperture and protoconch morphology are unknown, which makes it currently impossible to confidently place this species in any gastropod family.

Stratigraphic and geographic range.—Tithonian (Upper Jurassic) seep carbonates at NW Berryessa in the Great Valley Group, California, USA.

Figures

Fig. 5. Late Jurassic and Early Cretaceous abyssochrysoids Hokkaidoconcha spp. and Abyssochrysos? giganteum sp. nov. from seep carbonates in California, USA. A–C. Hokkaidoconcha occidentalis (Stanton, 1895). A. Lectotype (USNM 23077) from Paskenta (Tithonian; site 2). B. Specimen (CAS 70391) with well−developed spiral sculpture from Wilbur Springs (Hauterivian; site 5). C. Specimen (UCMP 555091) with poorly developed spiral sculpture from NW Berryessa (Tithonian; site 10). D, E. Hokkaidoconcha tehamaensis sp. nov. from Paskenta (Tithonian; site 10). D. Holotype (UCMP 555092); apertural (D1) and lateral (D2) views. E. Paratype (CAS 70390), note fading axial ribs on flank.F, G. Hokkaidoconcha morenoensis sp. nov. from Moreno Gulch (Santonian; site 14) F. Holotype (LACMIP 13483) with well−developed axial ribs and spiral sculpture on base. G. Paratype (LACMIP 13484) with fading axial ribs on later whorls. H. Hokkaidoconcha bilirata sp. nov., holotype (UCMP 555093) from Wilbur Springs (Hauterivian; site 5). I. Hokkaidoconcha sp. (UCMP 555094) from NW Berryessa (Tithonian; site 10). J, K. Abyssochrysos? giganteum sp. nov. from E Berryessa (Lower Cretaceous; site 12). J. Holotype (UCMP 555095). K. Paratype (UCMP 555096).