98 TERTIARY AND QUATERNARY PECTENS OF CALIFORNIA. 



Dimendons. — Alt. 56 mm.; long. (53 mm.; diam. 15 mm.; hinge line 28 mm. 



This species is readily distinguishable from P. atearnsi'i and /'. diegendh by 

 its smaller size, greater convexity of lower valve, and fewer ribs. Distinguishable 

 from P. Jx'lluK )\v smaller size, flat or concave upper valve, and narrow, more 

 elevated and prominent, radiating ril)s. Common in the upper horizon of the 

 Pliocene at Pacific Beach, and also in the strata exposed on Tenth street, near 

 Russ School, San Diego. 



RANGE. 



Pliocene. Temescal Canyon, north of Santa Monica, Los Angeles County 

 (Rivers); Pacific Beach, Russ School, and "San Diego well," San Diego 

 (Hemphill, Dall, Arnold). 



Pectkn (Pecten) lecontei n. sp. 

 PI. XXXIII, figs. -J, 4<r, and 4/-. 



Dencrlption. — Shell averaging about tiO millimeters in altitude, longer than 

 high, plano-convex, equilateral, and with smooth margins; base evenly rounded; 

 sides concave above. Right valve convex, and ornamented by about IS prominent 

 round-topped, peipendicular-sidcd, smootliish ribs, separated by interspaces, which 

 are narrower than the ribs and have nearly flat bottoms; surface .sculptured by 

 fine wavy incremental lines, which are generally worn oif from the tops of the 

 ribs; hinge less than one-half the length of the disk; ears somewhat convex; 

 the anterior with 2 or ?> bi'oad, nearly obsolete, radiating ridges, imbricating 

 incremental lines, and a rather small byssal notch; the posterior rectangulai'ly 

 truncated, and with fine incremental sculpture. Left valve flat or slightly concave, 

 ornamented by about 17 prominent rounded ribs, which are separated by inter- 

 spaces about equal in width to the ril)s; surface sculptured by luunerous fine, 

 sharp, regular, raised, incremental lines; ears conca\'e, rectangularly truncated, 

 and covered by fine sharp incremental lines. 



D!ni<'iisliinx.^-X\i. 59 nun.; long. fi5 mm.: hinge line 29 mm.: diameter IS 

 mm.; umbonal angle (left valve) 102 . 



This species is distinguishable from I\ diegtmxlH, P. iellus, P. dearnsii and 

 other members of this group by the number and convexity of the ribs on the 

 right valve. The left valves of /'. leconti'i and P. (I/effens/'f: are somewhat similar, 

 although the former has fewer ribs and is generally slightly more concave. 



P. lecontc! has so far been found only in the Pliocene of Cerros Island, where 

 it is associated with P. reatrhH^ P. eerroncns/ii, and Osfrea veatc/iii. The type is 

 now in the collection of Delos Arnold. Named in honor of the late Prof. Joseph 

 Le Conte, of the Universitv of California. 



Pliocene. Cerios Island, Lower California (University of California). 



