32 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 23 



shell as right valve, layer also extending beyond entire margin except 

 above hinge line; 6 to 8 prominent rows of concentric lamellae on disk 

 in very young stage, in adult stage either faintly present on umbo only 

 or entirely absent ; very minute concentric lines of growth on rest of disk. 

 Anterior auricle slightly shorter than that of right valve, with numerous 

 faint radial ridges and 4 or 5 fine concentric lamellae near the beak. 

 Posterior auricle same length as that of right valve and also pointed, 

 having numerous faint radial ridges. Color of right valve: white or 

 yellow-white ; left valve : White or yellow-white, with streaks or blotches 

 of yellow or yellow-brown. 



Holotype: Height and length 3.75 mm; diameter 1,5 mm; hinge 

 line 3.75 mm; Allan Hancock Foundation. 



Type locality : Off north side of Gorgona Island, western Colombia, 

 in 32 fathoms; Hancock expeditions bottom sample 584; February 24, 

 1938. 



The species also occurred in Octavia Bay, western Colombia, in 75 

 fathoms; Hancock bottom sample 555 ; January 27, 1938. 



Remarks: This species is quite distinct. From its nearest relative, 

 Cyclopecten pernomus (Hertlein), it can be separated particularly by its 

 transparent margins but also by its orbicular disk, absence of radial 

 ridges on the left valve, much finer concentric ridges on the right valve 

 and the length and sculpture of the auricles. From C. cocosensis (Dall) 

 it differs primarily in the transparent margins and also in the shape of 

 the disk, the absence of radial striae and posterior sulcus on the right 

 valves, and the length and sculpture of the auricles. 



Cyclopecten pernomus (Hertlein) 1935 

 Plate 11 



Pecten (Cyclopecten) rotundus Dall, 1908, p. 404. "Albatross station 

 2799, in Panama Bay, in 29'/2 fathoms; also at station 2784 [off 

 southern Chile, 48°4rS, 74°24'W; a single valve], in 194 fathoms, 

 mud, bottom temperature 51°. 9 F." 



[raora] Pecten rotundus von Hagenow, 1842, p. 554. Fossil; in chalk on 

 Baltic Sea island of Riigen, Germany. 



[raow] Pecten (Cyclopecten) cocosensis Dall. Hertlein, 1935, p. 319, pi. 

 18, figs. 7, 8. San Jose Island, Gulf of California, to Acapulco Bay, 

 Mexico, and near Cocos Island, Costa Rica. = P. pernomus Hert- 

 lein, non P. cocosensis Dall, fide Hertlein & Strong, 1946, p. 62. 



Pecten (Cyclopecten) pernomus Hertlein, 1935, p. 320, pi. 18, figs. 11- 

 13. Panama Bay; (?) Straits of Magellan; new name for Pecten 



