Atresius liratus Gabb, 1869

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 : 691-693

Atresius liratus Gabb, 1869

Fig. 8A–F .

1869 Atresius liratus sp. nov.; Gabb 1869: 169, pl. 28: 50.

1894? Atresius liratus Gabb (?); Diller and Stanton 1894: 442.

1895 Atresius liratus Gabb ; Stanton 1895: 68–69, pl. 11: 6.

1906 Atresius liratus Gabb ; Cossmann 1906: 193, fig. 19.

1927 Atresius liratus Gabb ; Stewart 1927: 426, pl. 23: 3.

1938 Atresius liratus Gabb ; Wenz 1938: 893, fig. 2627.

2006 Atresius liratus of Stanton, 1895; Campbell 2006: 382, fig. 6F.

Material.— Two specimens ( USNM 23075 a, b) figured by Stanton (1895) from Wilbur Springs (site 5) and numerous specimens from Rocky Creek (site 7) .

Description.—Protoconch unknown. Teleoconch fusiform, moderately high spired, up to five whorls, apical angle 35– 40°; suture distinct, deeply incised; whorls almost flat−sided, slightly convex, or angular, often with steep shoulder, basal margin strongly angular to rounded; sculpture consists of four to eight spiral cords, uppermost one at edge of shoulder, lowermost at basal margin, these two are usually strongest, interspaces between cords two to three times as wide as cords; spirals are crossed by dense, opisthocyrt growth lines of variable strength, in few specimens growth lines develop into axial ribs of same strength as spiral cords; base with seven to ten spirals of various strength, sometimes with alternating strong and weak cords, interspaces as wide as cords or narrower; aperture angular lenticular, apical side pointed; columellar features unknown.

Discussion.—The high variability of the whorl profile in this species, ranging from rounded to bicarinate to almost flat−sided was noted by Stanton (1895). Stewart (1927) suggested that Stanton’s (1895) species may be distinct from Gabb’s (1869) holotype because growth lines and spiral cords were different. However, our material shows all transitions between the morphologies documented by Gabb (1869) and Stanton (1895), and we have no doubt that they belong to one and the same species. In addition, we document that this species was also variable regarding the strength of its growth lines, which develop into strong axial ribs in some specimens.

Stratigraphic and geographic range.—Valanginian to Hauterivian (Lower Cretaceous), in the seep carbonates at Wilbur Springs and Rocky Creek, Great Valley Group, California, USA.

Figures

Fig. 8. Gastropods of uncertain taxonomic position, Atresius liratus Gabb, 1869 and Bathypurpurinopsis stantoni sp. nov., from Early Cretaceous seep carbonates in California, USA. A–F. Atresius liratus. A. Specimen (CAS 70395) with broad shoulder, from Rocky Creek (Valanginian; site 7). B. Specimen (CAS 70396) from Rocky Creek, note fine spiral sculpture on shoulder. C. Specimen (CAS 70397) with strong axial ribs, from Rocky Creek. D. Large specimen (CAS 70398) with rounded basal margin, from Rocky Creek. E. Specimen (USNM 23075a) illustrated by Stanton (1895: pl. 11: 6). F. Another specimen (USNM 23075b) from Stanton’s lot with fewer but stronger spirals, and a more angular basal margin. G–L. Bathypurpurinopsis stantoni, from Cold Fork of Cottonwood Creek (Albian; site 1). G. Specimen (CAS 70399) with thin apertural fold and preserved siphonal column. H. Specimen (CAS 70400) with excavated aperture. I. Specimen (UCMP 555102) showing fine spiral sculpture and sinuous growth lines. J. Specimen (CAS 70401) with well−developed apertural fold, note the indented shell on the left. K. Holotype (CAS 70402). L. Smooth specimen (UCMP 555103) with excavated aperture.