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Species / Tessarolax Trinalis


Original Description of Tessarolax trinalis by Murphy & Rodda, 1960:

  • "Shell small, moderately thick, spire about height of shell; body whorl biangulate with two rounded carina-like spiral ribs at the angulations and a third midway between; the upper rib is slightly stronger than the lower ribs and all may be slightly beaded; a single secondary rib may be developed below the lower angulation; the surface of young specimens is covered by fine lirae, in the adult the ornamentation is mostly covered with callus; number of whorls is greater than 5; suture linear, faint; aperture narrow above, widening below (anterior part unknown); in adult specimens the posterior digitation rises along the upper part of the shell obliquely and attached to the spire for about ⅔ the length of spire and then is free of spire and directed away from aperture; anterior digitations not preserved; adult possesses tubercule- like knob of a turn back from the aperture, apparently a callus deposit."

Stratum typicum: Balds Hill formation, latest Albian to earliest Cenomanian, Cretaceous

Locus typicus: northwestern Sacramento Valley, near Ono, Shasta County, California, USA

Tessarolax trinalis Murphy & Rodda, 1960 in Saul & Squires, 2015; Holotype; Budden Canyon Formation, Bald Hills Member, latest Albian to earliest Cenomanian, Cretaceous; Coll. LACMIP, No. 9826; Copyright Natural History Museum of Los Angeles County.

Tessarolax trinalis Murphy & Rodda, 1960; Paratype; Budden Canyon Formation, Gas Point Member, Turonian or Coniacian, Cretaceous; Thin bed of conglomerate, on Roaring River, Ono, Shasta County, California; Coll. LACMIP, no. 9827; Natural History Museum of Los Angeles County.


  • Michael A. Murphy and Peter U. Rodda, 1960. Mollusca of the Cretaceous Bald Hills Formation of California: Part I, Journal of Paleontology Vol. 34, No. 5 (Sep., 1960), pp. 835-858

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