PLIOCENE PECTENS. 123 



allied form, havinii" only 16 or IT). /'. axhleijl is di.stiiignii.sh'il)le from P. cfrm- 

 sensis, with which it is g-enorally associtited, by tlie smaller uumber of ribs and the 

 longitudinal sculpture of the same. 



In the Third street tunnel, Los Angeles, P. aMeyi is associated witli the 

 following- fauna: Pccten opuntia, P. lufmnrltus, P. pedroanim, P. strMV/ixii, 

 GJyphi!< densiclathrata, JVkhsu n. sp. ■;. Macoma sp. indet., Area multicOHtata, 

 Lima iMiiMni, Buccinum sp. indet., JVeverita rccluziana^ Astarte sp., Priene 

 oreijonens'iK^ Oxtrea veatcJui^ Pleurotoma sp. indet., carditoid, coral, bird bone, 

 crab's claw. This association of species indicates a horizon of the lower Pliocene. 



A fragment of a large specimen of /'. a.y/ilei/i was found by Doctors Dall 

 and Stearns in the low hills across the mesa three-fourths of a mile northeast of 

 Pacific Beach, near San Diego. 



P. lU-hlci/i is also found in the Pliocene at Cerros Island and San Fernando. 

 The type is from Cerros Island, and is now in the collection of the University 

 of California. Named in honor of Dr. (i. II. Ashley, of the United States 

 Geological Survey, whose pioneer work in the Santa Cruz ^Mountains added 

 greatlv to the knowledge of the West Coast Tertiarv. 



Pliocene. Cerros Island, oti' Lower California (Univ. of Cal.): Temescal Canvo;i, 

 Santa Monica Mountains. Los Angeles County (Rivers); Third street tunnel, 

 Los Angeles (Hamlin); near Pacific Beach, San Diego (Dall, Stearns): San 

 Fernando. Los Angeles County (Ashley); Cosmalia, Santa Barbara County 

 (F. M. Anderson): Olinda, Puente Hills, Orange County (Eldridge). 



Pegten (Plagioctenium) cereosensis Gabb. 



PI. XLIV, lig. 6- PI. XLIX, figs. 1, la, and \l,. 



1869. Pecten ccrrosensis Gabb, Pal. ('al., vnl. 2, 1S69, p. 32, pi. 9, figs. .55, 55a. 



1898. Pecten cerroaeims (Ta)il), Ball, Trans. Wagner Free Inst. Sci., vol. .3, pt. 4, 1898, p. 705. 



1898. Pecten {Phiffloctenium) suhrenirico.iKfi Dall, Wagnef Free Inst. Sci., vnl. H, pt. 4. 1898, p. 707 



pi. 29, fig. 8. 



190:>. I'ccten (Pluf/ioctenium) subventricosus Dall, Arnold, Jlem. Cal. Acad. Sci., vol. 3, 1903, j). 114. 



1904. Pecten suhventricoms Dall, Rivers, Bull. 8o. Calif. Acad. Sci., vol. 3, no. 5, \i. 69. 



1904. ''Pecten rentricosiis Snwerby, Rivers, oji. Ht., p. 69. 



Demri.pthm. — Adult .shell averaging about KlO millimeters in altitude, souK'what 

 longer than high, subequiyalve, biconvex, inequilateral, being somewhat obliquely 

 produced posteriorly; margins more or less sharply serrate; sides nearly straight 

 and sloping- at a rather steep angle. Right valve slightly less convex than left, 

 with l'1 to 23 prominent rounded, smooth-topped ribs, which in tlie adult broaden 

 and become ornamented above with looped incremental lines near the periphery 

 of the disk; interspaces considerably narrower than the ribs, with sloping- sides 

 and flat, naiTow bottoms, which are ornamented by a dense fringe of fine, sharp 

 concentric lamelhi?; hinge line a little more than one-half as long as disk; anterior 

 ear slightly longer than posterior, and ornamented by ridges and numerous 

 imbi'icating concentric lines; byssal notch of medium size; posterior ear nearly 



