COMPLETE GRAU : PECTINIDAE OF THE EASTERN PACIFIC 153 



margin to disk; gently convex, with shallow concave area halfway be- 

 tween hinge margin and base of auricle; several faint radial ridges in 

 juvenile stage, obsolete at maturity; surface covered with fine concentric 

 lamellae projecting above hinge line. Left valve with pronounced depres- 

 sion of central area; 14 shallow ribs, rounded but somewhat flattened 

 on top; juvenile specimens with two narrow ridges adjoining each sub- 

 margin, ridges becoming almost completely obsolete at maturity; inter- 

 spaces wider than ribs. Both auricles rather large, concave, and with 

 margins slanting inward from hinge margin to disk; several indistinct 

 radial ridges present. Surface of disk and auricles covered with fine con- 

 centric lamellae, continuous and unbroken from hinge margin of anterior 

 auricle to that of posterior auricle; lamellae always inclined in direction 

 of margins. Color of right valve: disk mostly white, with pale brown 

 mottling on umbo ; auricles pale brown ; interior white, except for few 

 streaks or blotches of pink or rose along submargins and on auricles. 

 Left valve light brown, dark brown or rose, mottled with lighter and 

 darker colors ; auricles white, yellow-brown or rose-pink ; interior mostly 

 white, with dark brown or rose at ventral margin and blotches of brown 

 and purple along submargins and in umbonal area. 



Holotype: 44 mm in height and 49 in length; diameter 15 mm; 

 hinge margin 29 mm ; Allan Hancock Foundation. 



Type locality : Tagus Cove, Albemarle Island, Galapagos Islands, 

 in 10-18 fathoms, sand and shell; Hancock station 157-34; 0° W 08" 

 S, 91° 22' 38" W; January 15, 1934. 



This species also occurred at the following Galapagos stations: 143- 

 34, off Wenman Island, 100-150 fathoms, coral and nullipores; 147-34, 

 Tagus Cove, Albemarle Island, 30 fathoms, rock, coral, nullipores; 149- 

 34, same place, 20 fathoms, rock and nullipores; 172-34, Stephens Bay, 

 Chatham Island, 12 fathoms, rock, boulders, gorgonids; 182-34, off 

 James Bay, James Island, 30 fathoms, coarse sand; 201-34, off Gardner 

 Bay, Hood Island, 25-35 fathoms, rock. 



Remarks: This species is quite distinct from Pecten vogdesi Arnold, 

 although obviously related. The most apparent differences are the white 

 right valve, sharply angled auricles and number of ribs. Other distinc- 

 tions are the longer hinge line, less convex right valve, uninflated umbo 

 of that valve, absence of intercalary riblets on the left valve, profuse 

 lamellae on that valve and coloring of both valves. From P. hancocki it 

 can be distinguished by the length of the hinge line, larger and sharply 

 angled auricles, lower and flatter ribs of the left valve, number of ribs 



