Clark: The San Lorenzo Series of Middle California 131 



not specifically determinable and it is not even certain that they are 

 the same species as the specimen obtained at locality 1131. 



Family Pectinidae 

 Genns PECTEN Midler 



PECTEN (LYEOPECTEN) GABBI, n. sp. 

 Plate 15, figures 1 and 2 

 Type specimen 11138, Coll. Invert. Palae. Univ. Calif., loe. 1311 

 Shell fairly large, heavy, equivalved ; right valve flat ; left valve convex. 

 Apical angle about 100°; dorsal edges very nearly straight; ventral edge rather 

 strongly convex. Left valve sculptured by about nineteen prominent and variable, 

 rounded radiating ribs; on the type specimen, a left valve, seven of these ribs 

 are heavier than the others ; one radiating from the beak down to the middle 

 of the ventral edge, three of the other ribs being anterior and three posterior 

 to this; in each interspace between these major ribs is a less prominent and 

 narrower rib, and in the interspaces between this narrower rib and the major 

 ribs on each side of it is a still less prominent and more narrow rib ; besides 

 this, in some of the interspaces, there is a fourth set of ribs still less prominent 

 than the others. The valve originally had strong and beautiful imbricated 

 sculpturing, which does not show on the type specimen but is seen on some of 

 the external easts. Ears large and heavy. One specimen of a cast of the anterior 

 ear shows eight or nine radiating ribs ; the ones next the dorsal margin being- 

 much finer than the others; surface of ear strongly imbricated. Eight valve 

 flat, sculptured by nineteen or twenty fairly heavy, rather broadly rounded, radiat- 

 ing, somewhat variable ribs; as on the left valve there is a tendency for some 

 of the ribs to be heavier than the others, but this difference is not so great nor 

 is the distribution of the heavy ribs so regular ; apparently there were no riblets 

 in the interspaces. Surface of right valve sculptured by imbricated incremental 

 lines, which are coarser than on the left valve. Sculpturing of ears of right 

 valve not preserved. 



Dimensions. — Type specimen: height, about 55 mm.; length, about 46 mm.; 

 diameter of both valves, about 37 mm. 



Occurrence. — University of California locality 1311. 



This form appears to be related to Pecten perrini Arnold, 105 which 

 is very common in the Vaqneros, the Tnrritella inezana zone, of the 

 southern part of the state. P. perrini is a very variable species, the 

 sculpturing being more irregular than on P. gabbi; it has about the 

 same number of ribs, and on some specimens certain of the ribs stand 

 out more prominently than others, as is the case with P. gabbi. The 

 imbricated concentric sculpturing appears to be much stronger on 

 the former, is more irregular, and the inter-ribbing and striations are 

 heavier. 



los F or original description of P. perrini, see U. S. Geol. Surv., Prof, paper no. 

 47, p. 80, pi. 14, figs. 1, la; pi. 15, fig. 1, 1900. 



