MIOCENE PECTENS. 91 



sculpture of luunerous faint radiatiny- ribs, inirroseopic stria?, and numerous more 

 or less prominent lines of interrupted growth were plainh- seen. The sculpture 

 was very similar, if not identical, to that of P. rioidol^yh!. P. pedroanux and 

 P. nwdolphl are also alike in shape and general characteristics, and tlie only 

 difference noted in a comparison of the two was the slightlj' larger size and more 

 prominently undulated disks of the former. A careful examination of better 

 material of the fossil form, if any is ever obtained, may lead to a union of the 

 two species. 



The Third street tunnel beds are of soft bluish siiale, which yielded besides 

 P. jh'dnKUMx \\\% loMow'vix'g fauna: Pecten ashlei/i, P.'sfMmsli, P. opimtia, Glypliix 

 densielathratti, Pectei) hitidiiritufi, JVcissa n. sp. ?, Mamma sp. indet., Area nvidfi- 

 costata, Lima hamlini^ Hucclnum sp. indet., Neverita recluziana, Artarfe^. sp.. 

 Pr'iene orego)ieii.'<!>i, (Mrea veatchii., PleurotoiKn sp. indet.. cai'ditoid, coral, IVird 

 bone, and crab claw. 



This fauna indicates a horizon about the saiue as that of the San Diego 

 formation, and is Pliocene (proba))!}* lower) in age. It thci'cfore seems likely tliat 

 P. pedroaiiim^ which has hei-etofore been considered a typical Monte re j' or middle 

 Miocene species, also occurs in the Pliocene, and may possibly be Dall's recent 

 deep-water species, P. raudolplii. 



liAXCK. 



Pliocene (lower). C'lark estate, Los Angeles and Pueute Hills, Los Angeles 

 County (Watts); Third street tunnel, Los Angeles (Hamlin): Joyce wells, 

 Whittier district, Puente Hills, Los Angeles County (Eldridge). 



Miocene. San Pedro (Trask, Gal)b); 4 miles south of McKittrick, Kern Countv 

 (Eldridge). 



Pecten (Propeamusium) stanfordensis n. sp. 

 PI. XXIII, %. 4. 



Description. — Shell axeragiug about i» millimeters in altitude, subcircular, 

 equivalve, equilateral, thin, onlj' slighth' ventricose, and with smooth margins. 

 Right valve with the exterior surface ornamented by numerous fine concentric 

 undulations and, in some cases, microscopic radiating striie; interior with 10 to 

 12 prominent, rounded, equidistant ribs extending from the umbo to or near to 

 the periphery of the disk, those ribs nearest the center of the shell being- 

 straight, while those near the sides are somewhat arcuate toward the central rib; 

 hinge line slightlj' longer than one-half the length of the disk; ears equal in 

 length, and ornamented by the fine concentric undulations; anterior ear with a 

 small byssal notch. Left valve similar to right, except that its anterior ear lacks 

 the bjrssal notch. 



Dimensions. — Alt. 7 mm.; long. 7.2 nun.; hinge line -1 mm.; diameter 1.2 mm. 



In the specimens showing the original shell luaterial the internal ribs some- 

 times break out and leave corresponding grooves in the disk, thus showing that 

 they are of a rather secondary growth compared to that of the disk. 



This species is somewhat similar to P. interradiatus of the Tejon (Eocene), 

 but may be distinguished from it by having 10 to 12 instead of 8 ribs, being 



