PLIOCENE PECTENS. Ill 



1-iblets (the middle riblet of thy three being slightly more prominent and spiny), 

 between which and the middle riblet of the adjoining interspace are two small 

 riblets (and sometimes another still smaller pair of intercalaries). while in the 

 adult F. hastatiis the fascicular arrangement on the right valve is obscure, there 

 lieing a central spiny rib with 2 and sometimes 4 faint scaly riblets between 

 the major rib and the middle riblet of the interspace. The fasciculi of the left 

 valve of P. heri('iiij< are convex, and consist of a central more or less spiny rib, 

 between which and the middle riblet of the fascicule of the interspace are about 

 !• to 12 thi-ead-like scaly riblets; while in /*. haxtafiitt there is a high narrow rib 

 with steeply sloping sides, having a top ornamented by numerous tall curved 

 spines; between this ril) and the rib running down the interspace are from three 

 to five faint thread-like scaly riblets. 



P. var. hericiux ranges from the Miocene (Santa Margarita formation) to the 

 Recent fauna. The fossil forms average smaller, and appear to have slightly more 

 scaly secondary riblets, Init in all other respects they are identical with the living 

 shells. 



A single specimen of Pecten, closely allied to if not identical with /'. var. 

 henc'kts, was found associated with /'. estre/la/iKs Conrad, Ostrca jMlmufa Cpr., 

 Tamiomma (jregarla Conrad, C'/iorii,^ helcheri Hinds, and Astrodapsw twaklux 

 Remond, near San Lucas, Monterey County. 



The type of /'. hericius is from the Strait of Juan de Fuca, off the north 

 coast of Washington, and is now in the U. S. National Museum (No. 5955). 



Living. Paget Sound (Dall, Carpenter, Button). 



Pleistocene (lower San Pedro formation). Deadman Island, San Pedro (Arnold). 



Pliocene. Temescal Canyon, Santa Monica Mountains, Los Angeles County 



(Rivers); Deadman Island. San Pedro (Voy. Arnold); Pacific Beach, San 



Diego (Hemphill. Arnold). 

 Miocene (upper). San Lucas, Monterey County (Handin, Arnold). 



Pecten (Chlamts) hastatus Sowerby var. hindsii Carpenter. 



PI. XLIII, figs. 1, 2, and 2f(. 



l.St)3. I'ecten hastatus (? var.) hindsii Carpenter, Brit. Assn. Rept., 1863, p. 645. 



1887. Pecten hericeus var. liiudsii Cai'penter, Whiteave.s, Trans. Roy. Soc. Canada, vot. 4, see. 4, 1887, 



p. 119. 

 1898. Pecten h<;riceiis var. hindsii Carpenter, Dall, Trans. Wagner Free Inst. Sci., vol. 3, pt. 4, 1898, 



p. 709. 



Description. — Shell smaller than /'. var. hertcius, averaging about 58 millimeters 

 in altitude; shape and convexity as in var. In'rk-iun; margins smooth. Right valve 

 with about 26 close-set, sometimes wide, flatfish, usually dichotomous, smooth ribs, 

 which show fine lines of growth on their surface; interspaces nai'row, channeled, 

 and sculptured by minute reticulations; hinge line one-half as long as disk; anterior 

 ear produced, sculptured by about six radials and prominently imbricating concentric 



