ARNOLD — THE PALEONTOLOGY AND STKATIGKAPHY OF SAN PEDRO. 109 



Section Chhivii/s s. s. 



Ribs small and numerous, imbricate or spinose; valves subequal, similar, oblique, or with 

 unequal ears, the [losterior smaller; Catnptoncctes striation and imbricate surface layer usually present; 

 shell usually solid and opaque; byssal notch and ctenolium present. 



Type, Peden islandicus (Miiller). 



27. Pecten (Chlamys) hastatus Sowerby. 



Plate XI, Fios. 4 and 4«. 



Pecten hastatus Sby., Thes. Conch., 1843, p. 72, PI. XXII, fig. 236 (not of Carpenter, Brit. Assn. 

 Rept., 1863, p. 645 = P. hcricetis Gld.); (? not of Gabb, Pal. Cal., Vol. II, 1869, 

 p. 104); (? not of Cooper, 7th Ann. Rept. Cal. St. Min., 1888, p. 257). Dall, Trans. 

 Wagner Inst. Sci., Vol. Ill, Part 4, 1898, p. 708. 



Shell similar in shape and general characteristics to P. hericeus. Left valve sculptured with 

 eight to ten prominent, narrow, convex, coarsely spinose, radiating ribs separated by interspaces 

 several times wider than the ribs; interspaces ornamented with fasciculi of small spinose ribs, which 

 in some cases have only the importance of spinose lines; anterior ear large, acutely pointed, with 

 three or four prominent, spinose, radiating ribs; right valve with eight to ten pairs of equally 

 prominent, coarsely spinose ribs, each pair separated from the next by deep rounded interspaces 

 along the bottoms of which run fine spinose lines; the members of each pair of ribs separated from 

 each other by interspaces about as wide as one rib, and also ornamented with spinose lines ; anterior 

 ear with four or five strong spinose ribs and separated from disk by deep notch ; posterior ears nearly 

 obsolete, radiately spinose. 



Dimensions. — Long. 54mm.; alt. 61 mm.; diam. 21 mm.: hinge 28 mm. 



Distinguishable from P. Jiericevn by the less numerous, but more prominent 

 and more strongly spinose radiating ribs. Dr. Dall^ says that Carpenter confused P. 

 hericcuH. with P. hastatus, and as Gabb and Cooper have probably used Carpenter's 

 P. "hastatus" as their type, their localities for that species would come under 

 P. hericeus. 



Mrs. Oldroyd has a beautiful pair of Pecten hastatus which was taken from a 

 fisherman's net at 8an Pedro. Dr. Dall identified this shell and said that it was the 

 first genuine P. hastatus that had ever been found at San Pedro. This species is a 

 northern form. 



Rare in Pliocene and lower San Pedro series of Deadman Island; one speci- 

 men from upper San Pedro series of Crawfish George's. The specimen figured is 

 from the Pliocene of Deadman Island, and is now in the collection of Delos Arnold. 

 Found also in the Pliocene at Packard's Hill, Santa Barbara, and Pacific Beach, San 

 Diego; and in the Pleistocene at the bath-house, Santa Barbara. 



Living. — San Pedro (Oldroyd; Raymond). 



Pleistocene. — San Pedro; Santa Barbara (Arnold). 



Pliocene. — San Pedro; Santa Barbara; San Diego (Arnold). 



1 Trana. Wagner Inst. Sci., Vol. UI, 1898, p. 708. 



