Pecten (Chlamys) wattsi 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. 120, pl. 11, figs. 1, 1a]
PECTEN (CHLAMYS) WATTSI n. sp.
Pl. XI, figs. 1 and 1a. «Description.— Shell averaging about 65 millimeters in altitude, slightly higher than long, equilateral, of medium thickness, decidedly ventricose, and with margins slightly finely serrate; base regularly rounded; sides sloping above, with slight concavity. Left valve with 5 high, rather narrow, rounded, almost smooth ribs, which are made prominently nodose by several very pronounced concentric undulations, or constrictions; interspaces much wider than ribs and each ornamented by about 5 small, subequal, rounded, imbricated riblets; whole surface of disk with a profuse, coalescent, microscopically checkered squamation; hinge line about two-fifths length of disk; anterior ear with arcuate end, and with surface sculptured by about 5. prominent imbricated riblets and several concentric undulations; posterior ear obsolete. Right valve about equal to left in convexity, with broad, flat-topped ribs and narrower interspaces, both being longitudinally sculptured by subequal riblets; ears similar to left; byssal notch not prominent; surface sculpture microscopic; constrictions less pronounced than in left valves.
Dimensions.— Alt. 67 mm.; long. 59 mm.; hinge line 20 mm.; diameter 36 mm. This species is even more· closely allied to P. swiftii Bernhardi (Jour. de Conch., voL 7, 1858, p. 90, pls. i and ii), of Japan, than is P. parmeleei. It is distinguishable from P. swiftii, however, by its broader ribs, not alternated radial riblets on the right anterior ear, and by the smaller number of secondary riblets in the wide interspaces. The specimens of P. wattsi are too poorly preserved to show satisfactorily the microscopic sculpture of the surface, but what is left of this sculpture appears to be very much like that of P. swiftii. P. wattsi differs from P. parmeleei in having broader and more strongly nodose ribs, more numerous (6 instead of 4) radials on the anterior ear, and most of all by the fewer and much larger-sized secondary radial riblets in the major interspaces. The poor state of preservation of the type of P. wattsi precludes any definite statements regarding its microscopic surface seulpture, but from as good a comparison as could be made under the circumstances the two species appear to have somewhat different kinds. P. wattsi is found in heds near Kreyenhagen's ranch, Fresno County, which are supposed to be of lower Pliocene age. It has been collected from beds of lower Pliocene age (Purisima formation) on Pescadero Creek, San Mateo County, and at other localities in the southern part of the State. At Olinda, Puente Hills, Orange County, Mr. Eldridge found P. wattsi associated with P. ashleyi, P. auburyi, P. oweni var., Priene (aff.) oregonensis, Cardium (cf.) quadrigenarium, Neverita recluziana, Phacoides californicus, and Fusus (cf.) barbarensis, in beds of probable lower Pliocene age. The type is from Kreyenhagen's ranch, Fresno County, and is now in the collection of the California Academy of Sciences. It is named in honor of Mr. W. L. Watts, whose collecting has added very materially to the list of west coast fossil Pectens. RANGE.
Pliocene (lower). Pescadero Creek, one-fourth mile above Jones Gulch, San Mateo County (Newsom; Arnold); Kreyenhagen's ranch, Fresno County (Watts); Olinda, Puente Hills, Orange County (Eldridge).»
RALPH ARNOLD, 1906
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R. Arnold, 1906, plate 11.
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