116 TERTIARY AND QUATERNARY PECTENS OK CALIFORNIA. 



1892. Pecten latimirilws C<jnrad, Williamson, Proc. l". S. Nat. Mu.s., vol. 15, 1892. p. 193. 



1898. Pecten {Chlamyn) latinvritiix Oonrail, Dall, Trans. Wagner Free Inst. Sci., vol. 3, pt. 4, 1898, 



p. 709. 

 1903. Pecten (Chlaiinis) Idlidiiriliiif C'onrad, Arnold, Mem. Cal. Acad. Sci., vol. 3, pt. 2, 1903, p. 



Ill, pi. 12, figs. 2 and 2u. 

 19114. Pecten tatiaiiritus Conrad, Keep, West Am. Sliells, p. 40. 



Description. — Shell averaging about 25 millimeters in altitude, about as long- 

 as high, inequivalve, compres.sed, inequilateral, disk oblique!}' produced posteri- 

 orily, thin; sides straight; margins smooth. Right valve more eoiiipressed than 

 left, with l!:i to Ki low. rather squarish ribs, separated b_y equal, more or le.ss 

 distinctly channeled interspaces; whole surface sculptured by numerous line con- 

 centric lines; liinge line nearly as long as disk; ears subequal in length; anterior 

 ear long and narrow, with .5 or (> prominent radials and numerous tine concentric 

 lines: byssal notch deep and distinctly .separating ear from disk; posterior ear 

 from rectanguhxrly to acutely pointed, sculptured l)y obsolete radials and concen- 

 tric lines. Left \'alve somewiiat more convex than right, otherwise similar to it; 

 anterior ear generally shorter and more prominently sculptured than posterior. 



DiiiicrixionK. — Alt. 2;") nun.; long. 23 mm.; hinge lin(> 20 mm.; diameter 9 nmi. : 

 iimliunal angle 90 . 



This species is cliaracterized l)y its small size, oblicjuc disk, tliinness, long 

 hinge line, and deep byssal notch. The .sculpture of the shell is usually well 

 marked. The ril)s are sometimes faintly medially sulcated, and the interspaces 

 sometimes contain a faint intercalary riblet in the later stages of growth. The 

 Pleistocene shells, as a rule, are rather more strongU' ribbed than the living. 



A pair of valves in the U. S. National Mu.seum (No. y«y64), from U. S. Fish 

 Conunission Station No. 2840, Santa Barbara Islands, is labeled ''/'. tmnbezenslx 

 Orb." This shell is ])robal)ly an albino variety of /'. latiaurifu.s, having just a 

 touch of color on the interior of the posterior ear of the left valve. The true 

 /'. Iiiiiihi'rienniv is from tlie i'ei-uvian part of the South American coasts. 



In the Third street tunnel, Los Angeles, /*. latiauritas has been found asso- 

 ciated with the following fauna: Pecten pedrominH^ P. asldeyi, P. (ipiintia, I*. 

 stenrnKii, (rh/plils denxlclat/initii. Xnxxa n. sp. '., Macinna sp. indet., Ai'ca multi- 

 (ioatata., Linxi hamlml, Bnccinnm sp. indet., Nevcrita Teclusiana, Astitrtc sp., Pr>en< 

 orcqonenx'ix, (Jsirea veatchil, Ph'iirotonia sp. indet., and a carditoid. As this fauna 

 indicates a horizon well down in the Pliocene, it extends the geologic range of 

 /'. htt'iiiiiritiix much further back than heretofore known. 



/'. latiaiiritiis is found living attached to kelp, those specimens inhabiting 

 the dcei)er, quieter waters being less stronglj' sculptured than those which are 

 subjected to a more strenuous existence nearer the shore. 



Living. Monterey (Yates); Santa Barbara to San Diego (Carpenter and others). 

 Pleistocene. Santa Barbara; San Pedro (Cooper): San Pedro; San Diego (Arnold. 



Wil.son. Dalll. 

 Pliocene. Third street tunnel. Los Angeles (Hamlin). 



