Euvola juanensis (Grant & Stevenson, 1948)
GRANT, U. S. IV & R. E. STEVENSON. 1948. A new Pecten from the Upper Miocene of California. Journal of Paleontology, 22: 804-805 [p. 804, pl. 124, figs. 1-4]
1948 Pecten (Pecten) juanensis Grant & Stevenson, 1948
U. S. Grant IV & R. E. Stevenson, 1948, plate 124.
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«Shell of moderate size; right valve highly ventricose; left valve flattish (none well preserved); right valve sculptured with 18 to 21 rounded ribs which are less convex near their medial portions though not flat, with evenly rounded interspaces which are somewhat narrower than the ribs; no interribs nor radial striations present on type material; ears of right valve about equal in length, smooth, with occasional subdued growth lines; byssal notch under right anterior ear slightly developed; hinge apparently similar or identical to that of Pecten coalingaensis. Dimensions of type: Height, 2 1/8 inches (54 mm.); width, 2 1/4 inches (57 mm.); ventricosity of right valve, 15/16 inch (24 mm.); length of hinge, 13/32 inch (27 mm.)
Holotype.— Catalogue No. 10441 in the collection at the University of California at Los Angeles; a Iarge right vaIve adherent to an echinoid, from UCLA locaIity 435, sandastone fossil reef on east side of valley of San Juan Creek, at elevation of about about 1500 feet above sea level, in west middle half of section 32, Township 28 south, Range 16 East (Mount Diablo Base and Meridian), eastern San Luis Obispo County, California. Stratigraphic position: approximately at conformable contact between lower and upper Neroly, in lower half of the upper third of the Miocene. U. S. Grant and E. H. Quayle, collectors, July 1933. Associated fauna: Lyropecten estrellanus, Astrodapsis sp. (at Locality 437, same horizon NW across valley) and Ostra panzana Conrad, etc. Paratype.— California Academy of Sciences, No. 7729, from UCLA Locality 438, in the same fossil reef about 3.6 miles North 29° West of UCLA Locality 435, sandstone, strike N29W, 85° northeasterly. Paratype.— U. S. National Museum, from UCLA Locality 435. This new species differs from Pecten coalingaensis Arnold of the upper Pliocene in its lack of rIbs on the ears of the right valve, in its lower, broader, less convex ribs with narrower interspaces, and in its greater ventricosity. Both species appear to have the same average number of ribs, which is about 20 on the right valve. From Pecten vogdesi Arnold, the new Miocene species differs in its smaller size, less ventricosity and smooth ears. Pecten vogdesi has 3 or 4 strong ribs on the right anterior ear with more, slightly less prominent ribs on the posterior ear. Both ears of the new Miocene species are smooth. The similarities between the new species and P. coalingaensis Arnold (Arnorld in Anderson 1905, p. 197; Arnold 1906, p. 97) is greater than the similarities between the new species and Pecten bellus Conrad (Proc. A. N. Sci. Phila. 1856, p. 312; Arnold 1906, p. 95). We believe that P. juanensis, P. coalingaensis and P. vogdesi are genetically related and form a clan to wich P. bellus is only related as a possible off-shoot fron the upper Miocene species here described, or from an earlier common ancestor. The matrix of the sorrounding sediment and the associated fauna indicate that P. juanensis probably was a dweller in shallow, warm water of normal salinity. The chief interest in this new upper Miocene species is that it appears to be ancestral to P. coalingaensis and P. vogdesi. Types of this new species were examined by Dr. Leo G. Hertlein of the California Academy of Sciences, an authorityon Pectens, who concurs with us in its distinctness from the other species mentioned above. Dr. Hertlein called our attention to the apical angle of the umbones, which in the new species is about 90 degrees, but in P. vogdesi is about 95 to 100 degrees. He also mentioned that Pecten heimi Hertlein (Proc. Calif. Acad. Sci. 1925, pp. 9-10.) of the lower Pliocene (?) of Lower California, Mexico has but weakly sculptured ears. In general appearances it closely resembles the new Miocene species which, however, has unsculptured ears. Possibly the relationship of the new species is closer to P. heimi than to P. vogdesi» ULYSSES SIMPSON GRANT IV & ROBERT EVERETT STEVENSON, 1948
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