Lituyapecten purisimaensis (Arnold, 1906)
ARNOLD, R. 1906. The Tertiary and Quaternary pectens of California. United States Geological Survey Professional Paper, 47: 1-264, 53 pls [p. 105, pl. 34, fig. 2; pl. 35, fig. 1, 1a]
1906 Pecten (Patinopecten) purisimaensis Arnold, 1906
R. Arnold, 1906, plates 34, 35.
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«Description.—Shell averaging about 125 millimeters in altitude, length same as height, valves both equally well compressed, equilateral, and with the margins smooth; base regularly rounded; sides relatively short, straight, sloping at a moderate angle. Right valve with about 24 prominent, T-rail-shaped ribs, flattened and sometimes faintly dichotomous above, overhanging deep, channeled, flat-bottomed interspaces, which are about equal in width to the ribs; whole surface of disk with incremental sculpture, which develops into prominent scales on the sides of the ribs; hinge line equal to about two fifths length of disk; anterior ear only slightly longer than posterior, sculptured by about three prominent radiating ridges and numerous imbricating incremental lines; byssal notch prominent, but not deep, being equal in width to one-half width of ear; posterior ear obliquely truncated, and ornamented by about three prominent radiating ribs and imbricating incremental lines. Left valve with narrow, rather sharp, concavesided ribs and wide concave-bottomed interspaces; surface with fine incremental sculpture; ears obliquely truncated and sculptured similar to those of right, except that the radiating ridges are finer and more numerous.
Dimensions.—Alt. 125 mm.; long. 125 mm.; hinge line 50 mm.; diameter 25 mm. This magnificent species is allied to P. coosensis and P. dilleri one of which is probably its precursor. P. prisimaensis is easily distinguishable, however, by the fewer and broader ribs on the right valve, narrower, sharper ribs and broader interspaces on the left, and from P. coosensis by the prominent radial sculpture of the ears. P. purisimaensis is characteristic of the Purisima (lower Pliocene) formation, where it is associated with P. healeyi, P. nutteri, Crepidula princeps, Phacoides acutilineatus, Rostellaria indurata, etc. The type is from the beds on the coast north of Pescadero, and is now in the collection of Delos Arnold. RANGE
Pliocene (lower), Purisima to Pescadero and Punta Año Nuevo, San Mateo County (J. P. Smith; W. R. Hamilton; Arnold).»
RALPH ARNOLD, 1906
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