160 AXEL A. OLSSON 



Pecten (FlabeUipecten) serlceus Hinds Plate 19, figures 3, 3a; 



Plate 21, figure 4 



Pecten sericeus Hinds, 1845, Zool. Voy. Sulphur, Moll., pt. 3, p. 60, pi. 17, figs. 1, la 



Bay of Panama. 

 Pecten (Pecten) sericeus Hinds, Hertlein, 1935, Proc. California Acad. Sci., ser. 4, 



vol. 21, No. 25, p. 303, pi. 18, figs. 14, 15; pi. 19, figs. 3, 4.— Hertlein and 



Strong, 1946, Zoologica, vol. 31, pt. 2, pp. 56, 57. 



Shell relatively large, thin, inequivalve, the beaks appressed or flattened 

 at the tip, the right valve of medium convexity, the left valv« depressed 

 and flattened. Both valves have about 24 ribs, the end ones small, only 

 about 20 produce flutings on the inner margin; in the right valve the ribs 

 are at first rounded, then trigonal, and finally becoming tricarinated at the 

 ventral margin, their interspaces as wide or wider, round or flat-bottomed; 

 in the left valve, the ribs are narrowly trigonal and low, their intervals much 

 wider and sometimes carrying an intercalated riblet near theii ventral mar- 

 gin; whole surface in both valves is overrun with close-set, raised, concen- 

 tric threads, at first regular, but on the lower half of the disk are more ir- 

 regular, sometimes crowded together, and divided into bands by resting 

 lines. Interior shows the flutings of the ribs in reverse, the interspaces be- 

 tween the external ribs form flattened ribs, their sides are thickened and 

 raised. Color is a pale light-brown or cream, faintly suffused with red on 

 the umbones. Ears of both valves relatively large and equal. 



Length 66.2 mm., height 63.4 mm., diameter 13.2 mm. 



Length 58.5 mm., height 56.2 mm., diameter n.4 mm. Arena Bank, Gulf 

 of California in 50 fathoms. Calif. Acad. Sci. 17715. 



I am indebted to Dr. L. G. Hertlein of the California Academy of 

 Sciences for being able to examine and photograph specimens of this fine 

 Pecten. Although widely distributed, the species is apparently rare and may 

 be obtained only by dredging. 



Range— Gu\{ of California to Ecuador. Mexico: Arena Bank, Gulf of 

 California; Santa Inez Bay; Gorda Bank; off Qarion Island (all Hertlein 

 and Strong). Costa Rica: Port Parker (H. and S.). Panama: Hannibal Bank 

 west of Coiba Island (H. and S.); near Cocos Island (Dall). Panama Bay 

 (Hinds). 



Genus LTROPECTEN Conrad, 1862 



Type species by subsequent designation, Dall, 1898, L. estrellanus 

 Conrad. Miocene of the Pacific coastal states. 



Shell large with convex valves, that of the left is slightly more inflated 

 than the right. Ribbed sculpture strong, formed by large, rounded or angular 

 ribs, their summits and intervals overrun by fine or coarse scabrous 

 longitudinal cords. Ears unequal, the posterior one smaller, the right an- 

 terior generally with a deep, byssal notch. 



Subgenus NODIPECTEN Dall, 1898 

 Type species by original designation, Pecten nodosus Linne. Florida 

 and the Caribbean. 



Shell usually large and coarse, both valves with nearly equal convexity 

 and similarly sculptured with large, corded ribs, often with nodes or humps 

 along them. 



