232 University of California Publications in Geology [Vol. 10 



right valve. Dimensions of type, which is a rather small specimen: 

 height, 31 mm. ; width, 24 mm. ; width of hinge, 13 mm. 



Occurrence. — At localities 2991, 2975, Pecten coalingensis zone, 

 upper Etchegoin Pliocene. 



PECTEN PROTEUS, n. sp. 

 Plate 6, figures 2, 2a, 2b, 2c 

 Type specimen no. 11089, Univ. Calif. Coll. Invert. Palae. 



Pecten deserti Conrad. Arnold, Ealph, U. S. Geol. Surv. Bull. 396, p. 76, 



pi. 26, figs. 3, 4, 1909. 

 Pecten deserti Conrad. Arnold, Ralph, and Anderson, Robert, U. S. Geol. 



Surv. Bull. 398, pi. 48, figs. 3, 4, 1910. 



Shell thin, equilateral, equivalve, compressed, with smooth regu- 

 larly convex margins. Dorsal margins slightly concave ; apical angle 

 about 95 degrees. Right valve ornamented externally by 21-24 wide, 

 moderately high, rounded ribs; on each side of major ribs is usually 

 a faint auxiliary riblet ; interspaces between major ribs less than 

 width of ribs ; anterior ear slightly longer than posterior, sculptured 

 by about five low radial ridges and indistinct incremental lines ; pos- 

 terior ear ornamented with about seven low, radial ridges and nearly 

 invisible incremental lines. Left valve in general similar to right, but 

 has higher, more strongly rounded, major ribs with narrow inter- 

 spaces ; anterior ear with about seven radiating lines. Dimensions of 

 rather small left valve of type : height, 37 mm. ; width, 33 mm. ; width 

 of hinge line, 17 mm. 



Specimens of this species found in the Coalinga region have here- 

 tofore been identified as Pecten deserti Conrad. On comparison of 

 P. deserti from the type locality at Carrizo Mountain, San Diego 

 County, with P. proteus, n. sp., several marked differences may be 

 observed. In P. deserti the ribs are higher, flatter above, with more 

 nearly vertical sides ; on the left valve the ribbing continues without 

 interruption from eai's over the outer depressed dorsal margins, while 

 in P. proteus, n. sp., the corresponding areas have no ribs. The ears 

 of P. deserti are larger, more strongly curved, and have less depression 

 where ears join dorsal margins of shell : also the dorsal margins show 

 less marked concavity. These instances can be better recognized by 

 seeing the comparative figures shown in this paper. 



Occurrence. — At localities 2991, 2975, with a large fauna charac- 

 teristic of the Pecten coalingensis zone, upper Etchegoin. 



