AKNOLD — THE PALEONTOLOGY AND STKATIGRAPHY OF SAN PEDRO. 103 



Typical form exceedingly common in the upper San Pedro series of San 

 Pedro, Los Cerritos and Long Beach; rare in the lower San Pedro series of Dead man 

 Island and San Pedro. Fonnd also in Pleistocene of Twenty-sixth street and Pacific 

 Beach, San Diego. 



Living. — Straits of Fuca to San Diego (Cooper). 



Pleistocene. — Benicia, Solano County; San Diego (Cooper; Arnold): San 

 Pedro (Arnold). 



Superfamily PECTINACEA. 

 Family IX. PECTINID.E. 



Genus Pecten Midler. 



Shell suborbicular, regular, resting on the right valve, usually ornamented with radiating 

 ribs; beaks approximate, eared; anterior ears most prominent; posterior side a little oblique; right 

 valve most convex, with a notch below the front ear; hinge margins straight, united by a narrow 

 ligament; cartilage internal, in a central pit; adductor impression double, obscure; pedal impression 

 only in the left valve, or obsolete. 



Type, Ostrea maximd Linne. 



Subgenus Pecten .s. s. 



Right valve moderately inflated, left valve flattish; sculpture of strong ribs with radial stri- 

 ation, more or less roughened by simple concentric lamellation or incremental sculpture; ears 

 subequal. 



Type, Pecten mn.ciinus Linne. 



[S. B.] Pecten (Pecten) bellus Conrad. 



Plate XXI, Fics. 1 and 2. 



Janira bella Conrad, Proc. Acad. Nat. Sci. Phila., 1S56, p. 312; Pac. R. R. Rept., Vol. VI, 1857, 

 p. 71, PI. Ill, fig. 16. Gabb, Pal. Cal., Vol. II, 1S69, PI. XVI, fig. 20. Cooper, 7th Ann. 

 Rept. Cal. St. Min., 1888, p. 244; not P. bellis McCoy {teste Dall). 



Pecten (Pecten) hemphitli Dai.1., Trans. Wagner Inst. Sci., Vol. Ill, Part 4, 1898, p, 706 (pars. ?). 



Pecten (Pecten) bet/us Con., Dall, Trans. Wagner Inst. Sci., Vol. Ill, Part 4, 1898, p. 704. 



Shell large, thin, inequivalve, elegantly, radiately ribbed. Left (upper) valve slightly convex, 

 the point of greatest convexity being generally about one-fourth the distance from the apex toward 

 the ventral margin; between this point of greatest convexity and the apex there is a deeply depressed 

 area, the depression generally not affecting the two outer ribs on each side, which inclose the depres- 

 sion on the sides; surface of left valve ornamented by thirteen or fourteen prominent, flat-topped, 

 sometimes faintly bicarinated, radiating ribs, which have flat, sloping sides; these ribs become broader, 

 less elevated and less sharply angulated near the periphery in the adult; interspaces slightly wider 

 than the tops of the ribs, with slightly rounded bottoms; whole surface of left disk covered with fine, 

 sharp, concentric, regular lamelkt; ears rather small, subequal, slightly concave, finely concentrically 

 lamellated, separated from the disk by an impressed line. Right (lower) valve prominently convex, 

 the point of greatest convexity being about one-third the distance from the apex to the ventral margin 

 of the disk; the umbo in this valve curves sharply and meets the plane of the ears at an angle of 



