COMPLETE GRAU : PECTINIDAE OF THE EASTERN PACIFIC 39 



(Fseudamusiumy vancouverensis Whiteaves, a living West Coast 

 species .... Although the radial ribs predominate, the "Camptonectes- 

 sculpture" is evident beneath them. 



Additional diagnosis: Shells very thin, translucent and uncolored; 

 without "ribs" (see below) ; left valve usually more convex than right; 

 height and length identical or nearly so; valves identical in size except 

 for Cyclopecten greenlandicus, in which right is smaller; disks occasion- 

 ally having obscure and vaiying number of low concentric folds in 

 umbonal region (in Hyalopecten folds are functional and more pro- 

 nounced, occurring throughout disk). Posterior auricles poorly defined; 

 in Cyclopecten greenlandicus their lateral margins are oblique, slanting 

 from submargin to hinge line, in all other species margins are continuous 

 with outlines of disks; ctenolium always present. Disks unsculptured 

 only in C. randolphi, other species having either concentric rows of 

 scales or vesicles, spinose radial ridges, or fine radial striae; right valve 

 never concentrically lamellated or ridged as in Cyclopecten, although C 

 vitreus has unique form of minute ridges. 



Remarks: Delectopecten differs from Cyclopecten s.l. in the shape of 

 the auricles, the unflexed right valve (except in Cyclopecten green- 

 landicus), the absence of concentric lamellae or ridges on that valve 

 (except in C. vitreus), the always-present ctenolium, and the transluc- 

 ency of all species. 



The author cannot agree with Woodring (1938, p. 35), who as- 

 signed Delectopecten subgeneric rank under Hyalopecten Verrill (1897, 

 p. 71). The latter was proposed as a genus, primarily because of the 

 concentric undulations of the disks ; while obviously separable from 

 Cyclopecten, its other similarities make it more appropriately a subgenus 

 under that unit. 



Arctinula is synonymized here because the slight distinctions between 

 its type and most species of Delectopecten are not felt to be of sufficient 

 importance to warrant separation at more than specific level. 



Since the type of Catillopccten, Pecten ?nurrayi, was one of the 

 species cited by Stewart, and since it agrees so well with the diagnosis of 

 Delectopecten, Iredale's genus is also synonymized. 



In addition to the species cited above and others included in this 

 paper, the following are also referable to Delectopecten : abyssorum 

 Loven (north Atlantic to West Africa and probably Mediterranean) ; 

 parvulinus Locard (Bay of Biscay) ; translucens and ?nicaceus Dautzen- 

 berg & Bavay (Makassar Strait, Indonesia) ; distinctus E. A. Smith 

 (Marion Island, Prince Edward Islands, South Indian Ocean). 



