COMPLETE GRAU : PECTINIDAE OF THE EASTERN PACIFIC 33 



(Cyclopecten) rotundus Dall, not P. rotundus von Hagenow. — 

 Hertlein & Strong, 1946, p. 61. Cedros Island, Lower California, 

 to Panama. 

 Cyclopecten pernomus (Hertlein, 1935). Keen, 1958, p. 72, fig. 135. 

 Cedros Island, Lower California to Panama. 



Holotype: U.S. National Museum, 



Type locality: Albatross station 2799, Panama Bay, Panama, in 

 29^2 fathoms. 



Original description : Shell very small, thin, white, suborbicular, with 

 subequal ears, both valves nearly equally convex; right valve polished, 

 minutely regularly concentrically striated, which sculpture is barely 

 visible under a hand lens; posterior ear smooth, anterior finely radially 

 threaded, with a narrow but clean-cut byssal sulcus and fasciole; left 

 valve finely sharply radially striated, the anterior ear finely reticulated, 

 the posterior apparently nearly smooth; hinge line short, straight; in- 

 terior smooth, a pair of small auricular crura present; the hinge line 

 with a minute central pit and two relatively large transversely sharply 

 striated, elongate areas representing a permanent provinculum. Height 

 and length, 3; hinge line, 2.5; diameter, 1.0 mm. A single valve from 

 near the Straits of Magellan, apparently the same species, measures 7 

 mm. in height. 



Additional descriptive notes: The right valve is slightly smaller than 

 the left. Its anterior auricle has concentric as well as radial striae ; its 

 posterior auricle is not "smooth," having 7 to 11 fairly prominent radial 

 threads and finer concentric threads. The posterior auricle of the left 

 valve is not "nearly smooth," having both fine radial and finer con- 

 centric threads. On about half of the hundreds of left valves examined 

 there were gray-brown, yellow-brown, red-brown or deep brown areas, 

 irregular and varying in size ; the right valves were all white. Specimens 

 measuring 10 mm in altitude were taken at Hancock station BS2130, 

 Pond Island, northern Gulf of California, in 62-85 fathoms; the largest 

 specimens previously recorded were 7 mm in altitude. 



Geographical range: Cedros Island, western Lower California, 

 Mexico, and Angel de la Guarda Island, northern Gulf of California, to 

 La Libertad, Ecuador. Also Guadalupe Island, Mexico (180 miles west 

 of central Lower California) and the Galapagos Islands. Ball's "single 

 valve from near the Straits of Magellan, apparently the same species, 

 . . ." cannot be accepted as conclusive evidence that Cyclopecten per- 

 nomus actually lives that far south. Previous records indicated San Jose 

 Island as the northern limit in the Gulf of California and Panama Bay 



