Chlamys proavus (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. 52, pl. 2, figs. 6-8]
1906 Pecten (Chlamys) proavus Arnold, 1906
R. Arnold, 1906, plate 2.
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«Description.— Shell averaging about 50 millimeters in altitude, much higher than long, compressed, subequivalve, and equilateral, except for the ears; base regularly rounded; margins smooth; sides straight and forming an acute angle at the umbo. Left valve with numerous more or less unequal, narrow, thread-like, imbricated ribs, between which are occasionally much finer intercalaries; interspaces about as wide as ribs, channeled and flat bottomed; whole surface of disk and ears ornamented by numerous, sharp, imbricating lamellrn of growth, which appear more prominently on the anterior portion of the disk; posterior ear short, slightly obliquely truncated, and sculptured by numerous radials and imbricating lamellae; anterior ear unknown, but probably much longer than posterior.
Dimensions. —Alt. 38 mm.; long. 30 mm.; hinge line (restored and approximate) 18 mm.; diameter 7 mm. This species is closely allied to P. traski Gabb, from the Cretaceous of the Pacific coast. It differs from the latter, however, in not having the diagonal microscropic sculpture so characteristic of that species. A fragment of a much larger specimen than the type of P. proavus, from the same beds and probably the same species, shows, near the periphery, narrow ridge-like ribs separated by rather wide interspaces in each of which are two or three fine thread-like riblets. (Pl. II, fig. 8.) The type of P. proavus, which is now in the collection of the department of geology, Stanford University, is a poorly preserved cast of a left valve on which part of the original shell matter is still preserved. It came from beds of probable lower Eocene (Martinez) age in the ridge between the headwaters of Pescadero Creek and San Lorenzo River, San Mateo County. At this locality it was associated with the following fauna: Terebratulina tejonensis, Tritonium (cf.) californicum, Patella (cf.) traski, Helcion dichotoma, Ostrea (aff.) idriaensis, Turbo sp., Acmaea or Patella sp., Terebratula n. sp., Cidaris (?) spines Semele sp. After an examination of the above fauna Doctor Stanton was of the opinion that it was younger than the Chico (Cretaceous). It is certainly not typical Tejon (middle or upper Eocene), but appears to be closer to the Martinez fauna than to any other, and is, therefore, tentatively placed in the horizon of the latter. RANGE.
Lower Eocene (Martinez?). Between the headwaters of Pescadero Creek and the San Lorenzo River, San Mateo County (H. S. Gay; Arnold).»
RALPH ARNOLD, 1906
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