COMPLETE GRAU : PECTINIDAE OF THE EASTERN PACIFIC 155 



off of interspaces, thus exposing a larger number of lamellae than are 

 visible on right valve. Interior of disk grooved as result of external 

 ribs, grooves becoming shallower toward umbo ; reverse surfaces of 

 interspaces flat and angulately ridged near ventral margin ; two small 

 nodules at base of anterior auricle and one rounded one with depressed 

 center at base of posterior ; cardinal crura as on right valve. Both auricles 

 same length as corresponding auricles of right valve and having varying 

 number of low riblets, most prominent near hinge line ; sculpture as on 

 disk, but with major portion of outer layer usually worn off. Color of 

 right valve: mostly white, w^ith umbonal area (and occasionally auricles) 

 pale orange to pink-orange; interior grooves white, reverse surfaces of 

 interspaces ecru, auricles and submargins pink or rose-pink. Color of 

 left valve: orange or red-orange (sometimes mottled with white) in 

 umbonal region, shading to pale brown or red-brown near ventral 

 margin; tops of ribs (on lower one-third to one-half of disk) pale ecru 

 or gray-white. 



Holotype: 47 mm in height and 49 in length; diameter 17 mm; 

 hinge line 22 mm ; Allan Hancock Foundation. 



Type locality : Chatham Bay, Cocos Island, Costa Rica, in 47 

 fathoms, coarse white sand; Hancock station 780b-38 ; 5° 33' 50" N, 

 86° 58' 45" W; January 14, 1938. 



The species also occurred off Nuez Island, Cocos Island, in 31-50 

 fathoms, coralline ; Hancock station 773-38. 



Remarks: This species is quite distinct from its nearest relative, 

 Pecten vogdesi Arnold. The most apparent differences are the white 

 right valve with pale orange or pink-orange umbo and the smaller 

 number of ribs, P. vogdesi having from 3 to 5 more. Other distinguishing 

 features are the oblique disk, shorter hinge line, less convex right valve, 

 less inflated umbo of that valve, rounded ribs and absence of intercalary 

 riblets on the left valve, complex surface sculpture and the exterior and 

 interior coloring. 



Although the holotype is the largest specimen found, it is not fully 

 adult ; judging by the other species in its subgenus it probably attains a 

 maximum height of from 70 to 80 mm. 



Apparently this species is restricted to the Cocos Island area. Pecten 

 vogdesi did not occur at any of the 7 Cocos Island Hancock stations in 

 1933 nor the 11 in 1938, and almost certainly does not live in the area. 

 However, it is plentiful off Costa Rica, a little over 300 miles eastward. 



In appreciation of the extensive support he has given marine re- 

 search, this species is dedicated to Captain Allan Hancock. 



