Hokkaidoconcha tehamaensis, Kiel & Campbell & Elder & Little, 2008

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 : 685-686

Hokkaidoconcha tehamaensis sp. nov.

Fig. 5D, E .

Etymology: After Tehama County, California, USA, county of the type locality.

Type material: Holotype: UCMP 555092 , specimen with the aperture and five whorls preserved; paratype: CAS 70390 , specimen with fading axial ribs.

Type locality: Paskenta (site 2), California, USA .

Type horizon: Tithonian (Upper Jurassic) seep carbonates, Stony Creek Formation, Great Valley Group.

Material.— Type material and four additional specimens from the type locality.

Diagnosis.—Shell slender turriculate, whorls straight−sided, with about 12 opisthocline, axial ribs that are usually tuberculate or spiny below suture; fine spiral threads vary from moderately well developed to absent; basal margin marked by thin spiral cords.

Description.—Teleoconch with at least five whorls and incised sutures; axial ribs are tuberculate and strongest on upper part of whorl, and may or may not disappear completely on lower half; growth lines strongly prosocyrt on basal margin and base, and end perpendicular to the margin of the aperture. Holotype 13 mm high and 4.5 mm wide.

Discussion.—This new species differs from the other Hokkaidoconcha species described here in having straight rather than convex sides, and the axial ribs are more tuberculate or spiny below the suture.

Stratigraphic and geographic range.— Type area only.

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).