Hokkaidoconcha bilirata, 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 : 686

Hokkaidoconcha bilirata sp. nov.

Fig. 5H .

Etymology: After its two prominent subsutural spiral cords.

Type material: Holotype: UCMP 555093 , specimen with the two last whorls preserved.

Type locality: Wilbur Springs (site 5), California, USA .

Type horizon: Hauterivian ( Lower Cretaceous ) seep carbonates, Great Valley Group .

Material.— Three specimens from Cold Fork of Cottonwood Creek (site 1), Albian.

Diagnosis.—Slender, high spired shell with straight to slightly convex whorls, sculpture of oblique to opisthocline ribs and spiral cords, of which the upper two are the strongest; basal margin gently convex, marked by disappearance of axial ribs and two or three strong spiral cords that give way to up to ten finer spirals on base. Aperture oval, inner lip smooth.

Description.—High spired shell with numerous whorls and an incised to grooved suture; 9–12 oblique to opisthocline ribs per whorl, and about 10 spiral cords, of which the apical two are strongest, more widely spaced than those below, and form tubercles at intersection with ribs; lower spirals subequal in strength and spacing, more strongly developed between axial ribs than on top of them; the basal margin is gently convex and marked by the disappearance of the axial ribs. Holotype with 2.5 whorls 11 mm high, largest specimen with 3.5 whorls 14.5 mm high.

Discussion.— Hokkaidoconcha bilirata differs from H. occidentalis by always having the two uppermost spiral cords well developed, whereas in H. occidentalis only the uppermost tubercle−forming spiral is well−developed.

Stratigraphic and geographic range.—Hauterivian–Albian (Lower Cretaceous) seep carbonates 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).