PLIOCENE PECTENS. 105 



it become:? necessary to rename the species, it is with pleasure that the writer is 

 enabled to dedicate it to Dr. William Healej' Dall. 



RANCiE. 



Pliocene. Purisima to Pescadero, and Punta AiTo Nuevo, San Mateo County (J. P. 

 Smith, Arnold); Temescal Canyon, Santa Monica Mountains, Los Angeles 

 County (Rivers); Pacific Beach, San Diego County, (Hemphill, Dall, Arnold, 

 and others); Tia Juana, Mexico (A. "W. Greeley); Brea Canyon, i miles south- 

 east ot Newhall, Los Angeles County (U. S. Nat. Mus.) 



Pecten (Patinopecten) purisimaensis n. sp. 

 PI. XXXIV, fig. 3; PI. XXXV, tigs. 1 anil Id. 



Description. — Shell averaging about 125 millimet(n-s in altitude, length .same 

 as height, valves both (>qually well compressed, equilateral, and with the margins 

 smooth; base regularly rounded; sides relatively short, straight, sloping at a mod- 

 erate angle. Right valve with about ^4 prominent, T-rail-shaped ribs, flattened 

 and sometimes faintly dichotomous above, overhanging deep, channeled, tiat- 

 bottomed interspaces, which are about equal in width to the ribs; whole surface 

 of disk with incremental sculpture, which develops into prominent scales on the 

 sides of the ri))s; hinge line equal to about two tifths length of disk; anterior 

 ear only slightly longer than posterior, sculptured ))y about three prominent 

 radiating ridges and lunuerous imbricating incremental lines; l»ys.sal notch promi- 

 nent, but not deep, Ix'ing equal in width to one-half width of ear; posterior ear 

 obliquely truncated, and ornamented by about three prominent radiating ribs and 

 imbricating incremental lines. Left valve with narrow, rather sharp, concave- 

 sided ribs and wide concave-bottomed interspaces; surface with tine incremental 

 •sculpture; ears obliquely truncated and sculptured similar to tiiose of right, except 

 that the radiating ridges are liner and more numerous. 



Dimemions. — Alt. 125 mm.; long. 125 mm.; hinge line 5t> nmi.; diameter 

 25 mm. 



This magnificent species is allied to P. coosens/'s and /'. (l/'i/c/-/. one of which 

 is proV)al)ly its precursor. /\ jiur/.s/'mae7isis is easily distinguishable, however, by 

 the fewer and broader ril)s on the right valve, narrower, sharper ribs and broader 

 interspaces on the left, and from I', eoosensk by the prominent radial sculpture 

 of the ears. 



P. jmrisunaenKiK is chai-acteristic of the Purisima (lower Pliocene) formation, 

 where it is associated with /*. healeyi, P. nutteri, Crep'tduhi. princeps^ Phacoides 

 (iei(tilhieati(n, Rostelliirid iiulnntta^ etc. 



The type is from the beds on the coast north of Pescadero, and is now in 

 the collection of Delos Arnold. 



Pliocene (lower). Purisima to Pe.scadero. and Punta Ano Nuevo, San Mateo 

 County (J. P. Smith; W. R. Hamilton; Arnold). 



