126 TERTIARY AND QUATP:RNARY PECTENS OF CALIFORNIA. 



l)eing somewhat obliquely produced; iniirgins sharply serrate; sides quite concave 

 above. Right valve with 19 to 21 squarish, close-set, smooth ribs, which, in the 

 adult, flatten out and have slopino- sides near the periphery of the disk; interspaces 

 very narrow and channeled; whole surface of disk sculptured by obsolete, wavy 

 lines of growth: hinot' line about t\\;o-thirds length of disk; ears e<{ual in length, 

 separated from disk 1)y a promiiuMit groove posteriorly anil small ridge antei'iorly; 

 anterior ear with -i rather faint radials. and numerous tine, imbricating incremental 

 lines; byssal notch deep, its upper side l)cing about parallel with the hinge line; 

 postei'ior ear with delicately curved extremity, and ornamented by iine incr(>mental 

 lines, and also on the lower half i)y faint radials. Left valve darker colored than 

 right, and with the ribs narrower, flat-topped, and having sloping sides; interspaces 

 wider, and covered lioth on the bottom and sides by tine, sharp, concentric lamelhe; 

 ears as in the right valve, except that the anterior one is not so conspicuously 

 notched. Hiuge strong, the pair of cardinal crura in the right vah e being exceed- 

 ingly well developed. Color patterns from light to dark brownish red. 



Dhneihv'onK. — Alt. It! mm.; long. 47 mm.; hinge line o2 mm.; diameter '.Vo mm. 



'I'his typical form is charactei'ized by its great and i-egular convexity, bi'oad 

 ribs, and strong hinge. Type from (lulf of California. 



Found living from the (xulf of California southward to Panama; in the Pleis- 

 tocene farther north. Erroneously reported from the Philippines by Sowerby. 



Living. Gulf of California to Panama (Sowerby, Carpenter, liutton); St. Elena, 

 off western coast of Colombia, South America (Sowerby). 



Pleistocene. San Pedro; San Diego; Lower California (Hemphill, Stearns, Orcutt); 

 Ventura: San Pedro; San Diego (Arnold); Springville, Ventura County 

 (Bowers). 



Pliocene (0- Cholas Valley, near San Diego (Stearns). 



Pecten (Propeamusium) uiversi n. sp. 



I'l. XLIV, fifrs. 8 and !i. 



Def!cription. — Shell averaging about 14 millimeters in altitude, about as long- 

 as high, circular in outline, ecpiilateral, compi'essed, white, translucent: margins 

 smooth. Right valve nmch compressed; surface .smooth except for numerous 

 very tine, regular, imbricating lamellw; hinge line one-half length of disk; ears 

 distinctly .separated from disk by impre.ssed line, subequal in length; the anterior 

 arcuate in fiont and with about 12 subeciual prominent radials and numerous 

 tine, regular, imbricating, incremental lamelhv; the posterior slightly obliquely 

 truncated and sculptured similarly to the anterior, except that the radials are 

 nearlj' obsolete; by.ssal notch of medium prominence. Interior of disk smooth 

 until an altitude of 15 millimeters is reached, when about 20 to 22 small, rounded, 

 radiating ribs appeal' and continue to the periphery. Left valve somewhat more 

 convex than the right, and ornamented externally by numerous unequal, 

 prominently imbricated ribs, the alternate ones being intercalated between 

 slightly larger one.s; whole surface sculptured by fine imbricating lamellae; 



