COMPLETE GRAU : PECTINIDAE OF THE EASTERN PACIFIC 35 



than left ; very numerous minute radial ridges crossed by more prominent 

 concentric lamellae which are higher over radial ridges, resulting in 

 scalloped effect; anterior auricle longer than posterior, with 10 to 12 

 rather faint radial ridges and 20 to 25 rows of more prominent con- 

 centric lamellae, the latter produced above hinge margin and appearing 

 in profile as spines; byssal notch moderately deep and no ctenolium; 

 posterior auricle slightly produced, with shallow sinus below, and having 

 6 major riblets nearest hinge margin, several minor ones adjoining disk, 

 and 8 to 12 rows of concentric lamellae. Left valve moderately convex 

 except for posterior ^ of disk, which is slightly flat or very shallowly 

 concave; 14 to 19 primary radial ridges, with 1 to 4 smaller intercalary 

 ridges between them, intercalaries beginning at various distances from 

 umbonal area; 22 to 40 rows of concentric lamellae, much more prom- 

 inent than those on right valve and, as on that valve, higher over radial 

 ridges, with resultant scalloped effect; anterior auricle moderately pro- 

 duced, with well-defined sinus below; 8 to 10 low radial ridges and 8 

 rows of fairly prominent concentric lamellae; posterior auricle slightly 

 produced, with shallow sinus below; 8 low radial ridges and 8 rows of 

 concentric lamellae. Interior of each valve flattened near ventral margin. 

 Both valves white or yellow- white ; left valve often with streaks or 

 patches of yellow, brown or red-brown, less frequently red or red-orange. 



On the holotype part of the posterior auricle of each valve is broken 

 off, giving the impression that no posterior sinus exists; a number of 

 single valves in perfect condition were found, and they show the actual 

 length of the auricles. 



Holotype: Height and length 3.5 mm; diameter 1 mm; hinge line 

 3 mm. Allan Hancock Foundation. 



Type locality: Off Wenman Island, Galapagos Islands, in 100-150 

 fathoms, coral and nullipores; Hancock station 143-34; 1° 23' 10" N, 

 91°48'45"W; January 11, 1934. 



Geographical range: Galapagos Islands; Callao, Peru, to Angel de 

 la Guarda Island, northern Gulf of California. 



Geochronological range: Recent only. 



Bathymetric range: 12 to at least 150 fathoms. 



Ecological data: Usually found on sand bottoms, occasionally rock; 

 associated with coral, coralline and nullipores. 



Remarks: This beautiful little species is quite distinct from any other 

 eastern Pacific Cyclopecten. As it occurred at 45 Hancock stations and 

 is so widely distributed, it seems remarkable that it remained so long un- 

 discovered. While this paper was in press Dr. Harald A. Rehder sent 



