Fissurella stantoni

Powell, Charles L. II & Geiger, Daniel L., 2019, Two new Miocene limpets (Fissurellidae) from southern California, with notes on other fossil occurrences of the family in northwestern North America, PaleoBios 36, pp. 1-7 : 2-4

FISSURELLA? STANTONI PoWELL AND GEIGER, N. SP. FIGS. 2, 5

Diagnosis — Fissurella? stantoni n. sp. differs from all other northeastern Pacific fossil and modern fissurel- lids by a combination of its large size, oblong-oval shape with divergent margins towards the posterior end, and lacking sculpture.

Holotype — LACMIP 14847.

Type locality —Locality LACMIP 31511 is from a prominent sandstone bed about 50 feet thick in the amphitheater on Old Topanga Road, Santa Monica Mountains, Los Angeles County, California. Collected by Bert Draper, date unknown. Coordinates are latitude 34.12502°, longitude -118.63786°. This site is from the Cold Creek Member of the Topanga Canyon Formation of lower to middle Miocene age (“Temblor” California provincial molluscan stage, =the uppermost Burdigalian/ Langhian stages of the International Commission on Stratigraphy stages).

Etymology —Named for Dr. Robert Stanton for his remarkable and continued work on California geology and paleontology.

Description

Known only from the type specimen. The shell has an incomplete margin but appears to be a long oval with lateral margins diverging slightly towards the posterior end. It is 55.9 mm long, 37.7 mm wide and 17.7 mm tall. The apex is located at about 60% of the length of the shell. The apex is of moderate height, has a small, squareoval foramen with a thickening around its margin and a steeper shell slope proximal to the foramen. The shell is without growth lines or sculpture and moderately thick. A profile through the apex and anterior and posterior margins show a slight concavity and then convexity between the anterior end and the apex, and a relatively straight profile between the apex and the posterior end.

Comparisons

Only a single fossil species of Fissurella occurs in Miocene strata of California, F. rixfordi Hertlein (1928) , which was described from the “Vaqueros” Formation near Crook Harbor on San Miguel Island, Santa Barbara County, however, it also occurs in the “Topanga” Formation of southern Orange County ( Stadum and Finger 2016). Fissurella rixfordi is easily distinguished from F.? stantoni by its smaller size, higher shells, and moderately strong radial sculpture. The only other Fissurella from California is the Pleistocene to Holocene F.volcano Reeve (1849) , which is easily distinguished by its smaller size, diverging lateral margins, and comparatively higher shell. The large shell size makes this new species most similar to Peruvian and Magellanic Fissurella (see McLean 1984), however, F.? stantoni is easily distinguished from all South American species in the genus by its narrower shell and small foramen.