130 TERTIARY AND QUATERNARY PECTENS OF CALIFORNIA. 



Dimensions. — Alt. 26 mm.; loiiy. 26 mm.; hiiioe line 2.5 mm.; diameter 7.8 mm. 



This variety is distinguishablt- from DalFs VAv'wty fu,cicolux, which it resembles, 

 by having a longer hinge line and generallj' more pointed ears. 



P'ound associated with the tj'pical species in the Pleistocene (upper San Pedro 

 formation) at San Pedro and San Diego. 



Pleistocene. San Pedro; San Diego (Arnold). 



Pecten (Chlamys) latiaukiti's Conrad var. delosi n. var. 



PI. XLVI, figs?. 9, 9r(, 10, and 10„. 



Descrijjfion. — Shell averaging about 12 millimc^ters in altitude, slightly longer 

 than high, subequivalve, botii valves only slightly convex, inequilateral, the disk 

 being decidedly oblique t,o the liinge line and somewhat produced posteriorly; sides 

 nearly straight; margins I'ough. Itight valve with about 16 prominent smooth- 

 topped sciuarish ribs; interspaces wider than the ribs. Hat-bottomed and ornamented 

 on tht> l)ottoni and sides by numerous prominent, regular. ei[uidistatit. imtjricating. 

 incremental lamelhe; hinge line as long as, or slightly longer than, the disk; ears 

 about equal in length; anterior ear long and narrow, separated from the disk Ijy a 

 deep, sharply defined, byssal notch and sculptured liy Kve or six prominent radials 

 and mimerous, regular, imliricating, incremental lamelhe. Left valve similar to 

 right except that the ribs are slightl}' narrower and the incremental lamelhe extend 

 over the tops of the ribs in some specimens; ears acutely pointed and sculptured by 

 numerous regular, sharp lamelhe; anterior somewhat shorter than the posterior and 

 with four major and as many intercalary radials; posterior with four or five radials. 



Dimensions. — Alt. 12 mm.; long. 12.5 nun.; hinge line 13..") nun. : diameter 3.5 

 nmi. ; umbonal angle itS"-. 



This beautiful little Peeten., one of the smallest found in our fauna, is charac- 

 terized by its extremely long hinge lin(> and prominently lamellated surface. It is 

 distinguishal>le from the typical /*. Jaiiaui'ifKs and varieties, with which it is allied, 

 b}' its longer hinge line and prominently lamellated int(>rspaces. 



The living specimens have the ribs more prominently lamellated above than the 

 fossd forms. /••. var. drJoni ajjpears to occupy somewhat deeper (and conse(iuently 

 colder) water than the typical form. The specimens of P. hitiaiiritiis found in the 

 Santa Barbara and ^Monterey regions appear to lean strongly toward this variety. 



P. delosi has been found fossil so far only in the lower fsan Pedro formation 

 (Pleistocene) at Deadman Island, near San Pedro. Types now in the collection of 

 Delos Arnold, the writer's father, after whom the species is named. Living speci- 

 mens dredged in 1.5 fathoms at Catalina Island. 



Living. Santa Catalina Island, Los Angeles County, in 1.5 fathoms (Arnold); Santa 



liarbara (Dall); .Monterey (Button). 

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



