118 TEKTIARY AND QUATEKNARY PECTENS OF CALIFORNIA. 



{/Kiritida Gabb. OalHoxfatii.a sp., Lunatiu lewis!/ Gould, (lli/ci/oif/'lx (+ Perl unruliix^ 

 near patxdam QiOwxwA., (rlycymerls a^., Yenei'leardla reiifrleoxn Gould. Pectrii laii\^oiil 

 n. sp., Pecteii ashleyl n. sp., etc. 



Named iu honor of Dr. A. C. Lawson, professor of geology at the University 

 of California. 



Pliocene (lower). Waldorf asphalt mine. J- miles south of (iuadaloupe. and i mile 

 north of Schumaim switch. Santa Barbara County (F. M. Anderson). 



Pecten (Ciilamys) oi'Untia Hall. 



PI. XLI, tiff. 2. 



l.SHS. Pi'rieii [Chliiiinix] opiiiithi Dall, Trans. AVagner Free Iiist. Sci., vdl. :!, pt. 4, 1.S9S, p. 707, pi. 29, 



fig. (). 

 190H. IWIni {('lilaiiiijx) npiniliii. J)all, .Vrnold, Jlem. Cal. A<:ail. Sci., vol. .'i, ISilS, p. li:i. 



JJexerlj/lloii. — Shell averaging- about 35 millimeters in altitude, slightly shorter 

 than high, suluMpuvalve. equilateral (except for ears), tioth valves nearly flat until 

 altitude of about 20 to 25 millimeters is reached, when they grow more convex: 

 contracted at basal margin when adult; sides only slightly conca\e above. Right 

 valve with 4<i to (>0 subequal, narrow, iml)ricated, more or less dichotomous ri])s, 

 which are separated by channeled interspaces aV)out e((ual in width to the ribs: 

 hinge line about two-fifths as long as disk; anterior ear much produced, sculptured 

 by about six promiiuMit. sharjily iml)ricated radials, and imbricating incremental 

 lines; by.ssal notch (juite prominent; posterior ear nearly obsolete, radiall}* and 

 concentrically sculptured; whole surface of disk and ears sometimes microscopically 

 checkered or tessellated. Left valve similar to right. 



DliiieiiKliius. — Alt. -i;:! nun.; long. -10 mm.; hinge line Kl mm.; diameter 12 nun.; 

 umljonal Mugle 78'. 



This species is allied to /■'. hasfatuH var. iiavurvhits, fi-om which it difl'ers l)y its 

 smallei' and not fasciculated radial ribs, more elongated anterior ear, more densely 

 radially costate posterior ear, small size when adult, and by a tendency to be 

 suddenly contracted at the basal margin on the completion of growth. /'. upHidld 

 is distinguishable from otlu'r memljers of this group by its large number of nearly 

 ecjual thread-like ribs and small umbonal angle. 



Pliocene. Pacific Beach, San Diego (Hemphill; Hamlin; Arnold); Packard's Hill, 

 Santa Bar))ara (J. H. Wilson, Arnold); Rincon Creek. Santa Barbara County 

 (Watts): Tiiird Street tunnel, Los Angeles (Hamlin): Teinescal Canyon, Santa 

 Monica Mountains, Los Angeles County (Rivers). 



