COMPLETE GRAU : PECTINIDAE OF THE EASTERN PACIFIC 29 



Cyclopecten catalinensis (Willett) 1931 

 Plate 9, fig. 1 



Pecten (Cyclopecten) catalinensis Willett, 1931, p. 65, pi. 4, figs. 1-2. 

 — Hertlein & Strong, 1946, p. 61 ; Catalina Island, California, to 

 Cedros Island, Lower California. 



Holotype: Los Angeles County Museum, Los Angeles, California. 



Type locality: Off White's Landing, north side of Santa Catalina 

 Island, California, in 100 fathoms. 



Original description: Shell small, shining, transparent, very fragile; 

 right valve v^^hite, unmarked; left valve w^ith about tvi^enty, somewhat 

 irregular, brown, radial rays, running from the median part of the disk 

 to the margin; these rays show through the transparent shell so plainly 

 that, to a casual inspection, the right valve appears rayed also. Ventral 

 margin of left valve convex; that of right valve flexible and reflexed 

 when closed. Sculpture of left valve consisting of fine growth lines, 

 crossed in the umbonal region by very fine, wavy striae, visible only 

 under a strong lens. Ventral two-thirds of right valve marked by fine, 

 closely spaced, incised, concentric lines, with wider interspaces; similar 

 lines also apparent on the anterior auricle above the rather shallow byssal 

 notch. Ears in both valves nearly equal in size. On the left valve the 

 ridges running from the sides of the shell to the umbo, and dividing the 

 discal from the auricular regions, are so sharply defined as to be almost 

 carinate; these ridges, meeting at the umbo, form the two sides of a 

 perfect triangle. 



The type measures in millimeters : height, 7 ; breadth, 7.5 ; hinge line, 

 5 ; diameter, 1.6. 



Additional descriptive notes: An interesting structural feature of the 

 right valve is shared by a number of other species of Cyclopecten and 

 Propeamussium in which that valve has a reflexed ventral margin: the 

 reflexed portion is thinner than the rest of the disk and so fragile that 

 it breaks off if one attempts to separate the valves of a closed specimen ; 

 consequently separated specimens appear to have a smaller right valve. 



The largest specimens known measure 9 mm in height and length, 

 and were taken by the Hancock expeditions off Tiburon Island, northern 

 Gulf of California. 



Geographical range: San Miguel Island, Santa Barbara Islands, 

 southern California, to Cedros Island, Lower California, Mexico; also 

 off Tiburon Island, Gulf of California. Previous records indicated 

 Santa Catalina Island, California, to be the northern, and Cedros Island 



