152 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 23 



purple just inside juncture with left valve; left valve various shades of 

 brown, purple-brown or rose-brown, with large white central area. 



Geographical range: Punta Eugenia, western Lower California, 

 Mexico, and entire Gulf of California, to Paita, Peru. Previous records 

 indicated Magdalena Bay, Lower California, as the northern limit in the 

 Pacific Ocean, but the Hancock expeditions extended it by about 300 

 miles. 



Geochronological range; Pliocene, Pleistocene, Recent. 



Bathymetric range: Recorded in 2 to 120 fathoms. 



Ecological data: Usually found in sand, sandy mud, or mud bot- 

 toms, associated with coral, coralline or sponge. 



Hancock Expeditions Collecting Stations: 

 ECUADOR: La Plata Island; 10 fathoms, bottom sample 500. 

 COSTA RICA: Cocos Bay, 2 fathoms, sand, sta. 116-33; Port Parker, 



5-10 fms., sandy mud, sta. 936-39. 

 GULF OF CALIFORNIA: 27 stations; 8-100 fathoms, sand, mud. 

 WESTERN LOWER CALIFORNIA: Punta Eugenia (farthest 

 north), 26 fathoms, rock, coralline, sta. 1260-41; 4 stations, 14-26 

 fathoms, rock, sand. 



Pecten (Oppenheimopecten) galapagensis sp. nov. 



Plate 56 



Shell inequivalve, thin and of moderate size, largest known specimen 

 (the holotype) 44 mm in height and 49 in length; left valve smaller 

 than right and recessed into that valve at ventral margin to depth of 4 

 mm ; hinge line well over half as long as disk. Right valve quite convex, 

 but less so than Pecten vogdesi Arnold ; umbo not produced above hinge 

 margin; 15 smooth and gently rounded ribs, with a very shallow riblet 

 adjoining each submargin ; interspaces narrower; fine concentric lamellae 

 covering upper half of disk, with very fine growth striae below. Interior 

 of disk with grooves corresponding to external ribs, becoming shallower 

 toward umbo; reverse surfaces of interspaces flattened and (near ventral 

 margin) angulately ridged; auricular crura next to submargins small 

 and elongate; cardinal crura low and flat. Anterior auricle rather large, 

 flat, and with margin slanting inward from hinge line to byssal notch ; 

 weak convex fold just above disk; 3 or 4 small radial ridges above 

 fold ; byssal notch shallow and ctenolium of 3 to 5 teeth ; auricle covered 

 with fine wavy concentric lamellae projecting above hinge line ; posterior 

 auricle rather large and high, with margin slanting inward from hinge 



