Parvamussium lajollaense (M. A. Hanna, 1927)
HANNA, M. A. 1927. An Eocene invertebrate fauna from the La Jolla quadrangle, California. University of California Publications, Bulletin of the Department of Geological Sciences, 16 (8): 247-398, pls. 24-57. [p. 277, pl. 32, figs. 1, 3-6]
1927 Pecten lajollaensis M. A. Hanna, 1927
M. A. Hanna, 1927, plate 32.
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«Cotypes.— Nos. 31106-07-08-09-10, Univ. Calif. 0011. Invert. Pal.; U. O. loc. 5062
Description of species from cotypes.— Shells quite small, thin; length and altitude about equal; slightly convex; base evenly rounded; sides, nearly straight to the beaks, forming an angle of about ninety degrees; left valve: hinge line three-fourths the length of the disc; ears sub-equal, the anterior the larger, radially ornamented by fifteen to twenty fine rounded ribs which are crossed by growth lines; disc ornamented by about sixty-five nearly equal sized, fine, rounded, linear ribs which are crossed by fine indistinct growth lines; right valve: ears unequal in size, posterior the smaller, anterior much produced, crossed by growth lines but not radial lines; surface of the disc sculptured by fine, prominent, equally spaced, concentric growth lines; radial sculpturing not present; internal ribbing of the right valve consists of ten prominent, narrow, rounded ribs separated by very much wider flat-bottomed interspaces.
Pecten lajollaensis n. sp. differs from Pecten interradiata Gabb⁵⁸ in not having the same sculpturing. The heavy internal ribs of the new species extend to the perifery of the shell, rather than only a short way down from the umbones. It differs from Pecten calkinsi Arnold⁵⁹ and Pecten landesi Arnold⁶⁰ in size, shape, and sculpturing.»
⁵⁸ P. interradiatus Gabb. Pal. Oalif., vol. 2, p. 199, pI. 33, figs. 98 and 98a, 1869.
⁵⁹ P. calkinsi. See P. (Chlamys) calkinsi Arnold. U. S. Geol. Surv., Prof. Paper 47, p. 51, pI. 11, figs. 1 and 2, 1906. ⁶⁰ P. landesi. See P. (Chlamys) landesi Arnold. Ibid., figs. 3, 4 and 5. MARCUS ALBERT HANNA, 1927
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«Comments.—The left valve (UCMP 31108) is sculptured by many (about 65) small, fine, almost equidimensional ribs; on the basis of type material, this characteristic separates P. Iajollaense from the other described Tertiary species of Parvamussium. The interior of the right valve (UCMP 31108) bears 10 prominent ribs that extend almost to the ventral shell margin.
Geographic range.— Middle to southern California. Geologic range.— Eocene. Occurrence in California.—Eocene: Ardath Shale and Muir Sandstone (Weaver, 1953).» MOORE, E. J. 1984. Tertiary Marine Pelecypods of California: Propeamussidae and Pectinidae. United States Geological Survey Professional Paper, 1228-B: iv + B1-B112, figs. 1-2, pls. 1-42. [p. B10]
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Parvamussium lajollaense (M. A. Hanna); E. J. Moore, 1984, Tertiary Marine Pelecypods of California: Propeamussidae and Pectinidae, plate 1, figures 12, 13.
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