AENOLD— THE PALEONTOLOGY AND STRATIGKAPHY OF SAN PEDKO. 107 



Subgenus Chlamys Bolten. 



Valves moderately inflated, subequal, in general similar (except in color); sculpture of 

 radial ribbing with or without Camptoyiectes striation, with or without an imbricate surface layer; 

 frequently spinose on the ridges; ears often discrepant, the posterior smaller. 



Type, Pecten islandicus (Miiller). 



Section Patinopeden Dall. 



Valves with small ribs, flat on the right valve and sometimes dichotomous; smaller and 

 more rounded on the left valve; concentric sculpture inconspicuous; radial stride absent or 

 obsolete; ears subequal ; valves nearly equilateral. 



T3'pe, Pecten cauiinus (Gld.). 



25. Pecten (Patinopecten) caurinus Gould. 



Plate XIII, Fig. 6. 



Peclen caurinus Gld., Proc. Bost. Soc. Nat. Hist., Vol. Ill, 1850, p. 345; Wilkes E.xpl. Exped., 

 Vol. XII, 1852, p. 458, fig. 569. Williamson, Proc. U. S. Nat. Mus., Vol. XV, 1892, 

 p. 193; T=: p. yessoeiisis Cpr., (non Jay, 1856); ^= P. propatulus Carpenter (non 

 Conrad, 1849) {Jide Dall., Trans. Wagner Inst. Sci., Vol. Ill, Part 4, 1898, p. 710). 



Amusium cauriuum Gld., Carpenter, Brit. Assn. Rept. , 1863, p. 645. Cooper, 7th Ann. Rept. 

 Cal. St. Min., 1888, p. 228. Keep, West Coast Shells, p. 168, 1892. 



Shell large, nearly circular, flat inequivalve, rather thin; right valve with twenty strong, 

 flat-topped, smooth, squarish ribs, with interspaces wider than the ribs ; left valve less conve.x than 

 right, with seventeen rather acutely rounded ribs, with wide, shallow interspaces ; surface of left 

 valve sculptured by regular, fine, undulating, concentric lines; ears not large, obliquely truncated at ends. 



Dimensions. — Long, no mm.; alt. no mm. ; diam. 16 mm.; hinge 46 mm. 



Tliis large, flat Pecten i.s distinguishable from the others of this genus found in 

 these deposits b}^ its size and shape. P. expansua Dall differs from this species by 

 having twenty-five to thirty dichotomous ribs. P. yessoensis from Amori, Rikonoken, 

 Japan, differs from P. caurinus by having a more convex shell, wider, lower, more 

 rounded ribs on the right valve, less prominent ribs on the left valve, and by hav- 

 ing larger ears, which are truncated more nearly at right angles at the ends. Pecten 

 jtrojMtulus Conrad is more convex and has fewer but stronger ribs and narrower 

 interspaces on the right valve. Specimens identified by Dr. Dall. 



Common in the Pliocene of Deadman Island and Timm's Point; rarer in the 

 lower San Pedro series of Deadman Island and San Pedro. Also found in Pleisto- 

 cene on beach near bath-house and in Pliocene at Packard's Hill, Santa Barbara. 

 The specimen figured is from the Pliocene of Deadman Island and is now in the col- 

 lection of Delos Arnold. 



Living. — Puget Sound (Carpenter). 



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



Pliocene. — Eagle Prairie, Humboldt County; San Fernando (Cooper). 



