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Species / Tessarolax Acutimarginatus


Original description of Tessarolax acutimarginatus by Nagao, 1932, p. 43:

  • "Shell semifusiform ; spire slightly higher than the aperture, with an apical angle of about 35, completely incrusted by a thick deposit so as to obliterate the sutures and ornamentation. Spire-whorls about seven in numbers; each whorl moderately convex, with an angulated shoulder and a slightly concave lower surface. Upper part of the spire bearing a varix-like process which is flattened on both sides and elongated vertically; this process originating above at a point about opposite to the outer lip and running obliquely backward and downward up to the upper margin of the penultimate whorl. Spire-whols ornamented with two spiral ribs, one on the shoulder and the other along the lower suture, besides numerous fine spiral striae all over. Body whorl rather short with convex sides, very acute at the periphery near the aperture; three spiral carinae on the surface above the periphery, of which the lowest one on the periphery itself is the broadest and becomes very prominent near the aperture. Base flat, low conical, ornamented with two distant spiral ribs in its upper portion, besides numerous crowded and fine spiral striae all over. Anterior canal broken, but apparently narrow; posterior canal ascending along the spire, long, its lower portion being preserved. Two apertural spines, originating each from the uppermost and lowest carina of the body whorl respectively, probably well developed, their greater part being lost; of these spines the lower one directed outward and downward."

Locus typicus: The vicinity of the Kawakami Coal-mine, Japanese Saghalin

Stratum typicum: Upper Ammonite Beds of Hokkaido Island, Cretaceous

Tessarolax acutimarginatus Nagao, 1932, pl. VI, fig. 10, 10a, 15, 15a-c

Specimens from private collections

aff. Tessarolax acutimarginatus Nagao, 1932; upper Ezo Formation, Santonian, Cretaceous; Haboro River Main stream, Haboro machi Tomamae county, Hokkaido, Japan; 70mm; Coll. Philippe Simonet

aff. Tessarolax acutimarginatus Nagao, 1932; Cretaceous; Inasato, Hubetsu district, Hokkaido Island, Japan; Coll. Ulrich Wieneke no. UW2314

aff. Tessarolax acutimarginatus Nagao, 1932; Santonian, Cretaceous; Haboro-Cho, Hokkaido Island, Japan; Coll. Ulrich Wieneke

aff. Tessalorax acutimarginatus Nagao, 1932; upper Turonian, Yezo Group, upper Cretaceous; Hokkaido Island, Japan; Coll. Laurent Zimmer



  • Nagao, T., 1932. Some cretaceous Mollusca from Japanese Saghalian and Hokkaido (Lamellibranchiata and Gastropoda). Journal of the Faculty of Science, The Hokkaido Imperial Univiversity Series 4. 2(1): 23-50.

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