Pecten (Plagioctenium) cooperi Arnold, 1906
ARNOLD, R. 1906. The Tertiary and Quaternary pectens of California. United States Geological Survey Professional Paper, 47: 1-264, pls. 1-53. [p. 124, pl. 49, figs. 2-4]
«PECTEN (PLAGIOCTENIUM) COOPERI n. sp.
Pl. XLIX, figs. 2, 3, and 4. Description.— Shell averaging about 30 millimeters in altitude, slightly longer than high, both valves moderately convex, disks slightly obliquely produced posteriorly, moderately thick; disk generally characterized by several more or less prominent concentric zones of interrumpted growth, which show as color bands even on the fossil shells; sides nearly straight; margins serrate. Right valve with 18 to 20 flat-topped, squarish ribs, which tend to flatten out and become more convex topped in the later stages of growth; interspaces narrower than the ribs, and crossed on the bottom by numerous, fine, sharp, incremental lirulae, which become obsolete on the ribs excepting in the later stages of growth; hinge line somewhat more than one-half length of disk; anterior ear slightly produced and ornamented by 4 or 5 prominent radials and numerous incremental lines; byssal notch deep and sharply defined; posterior ear slightly obliquely truncated, and sculptured by obsoIete radials and fine incremental lines. Left valve similar to right, except that the ribs are narrower and the interspaces correspondingly broader.
Dimensions.— Alt. 30 mm., long. 31 mm.; hinge line 17 mm.; diameter 12 mm.; umbonal angle 95º. This species is characterized by the number of its ribs and the concentric imbricating bands of interrupted growth. It is distinguishable from P. cerrosensis by its fewer ribs, less prominent lirulae on the sides of the ribs, and its prominent concentric bands of interrupted growth; distinguishable from P. circularis and varieties by its less ventricosity, fewer ribs, and its characteristic concentric sculpture. Specimens of this species were noticed in a box in the National Museum with P. subventricosus [ = P. cerrosensis] from Pacific Beach, San Diego. P. cooperi is so far known only from the Pliocene of Pacific Beach, near San Diego. Type and cotype now in the collection of Delos Arnold. Named in honor of the late Dr. J. G. Cooper, one of the pioneer paleontologists of the Pacific Coast. RANGE
Pliocene. Pacific Beach, San Diego (Hemphill, Arnold)».
RALPH ARNOLD, 1906
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R. Arnold, 1906, plate 49.
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