COMPLETE GRAU : PECTINIDAE OF THE EASTERN PACIFIC 7 



1054 through 1099: vol. 6, no. 3. 



1104 through 1176: vol. 6, no. 4. 



1177 through 1246: vol. 6, no. 5. 



2000 through 2079 : vol. 6, no. 1. 



2080 through 2141 : vol. 6, no. 3. 



2142 through 2169: vol. 6, no. 4. 

 For stations subsequent to 1942, complete data can be obtained from 

 the Allan Hancock Foundation, University of Southern California, Los 

 Angeles 7, California. 



Key to the eastern Pacific Genera and Subgenera 



1. Both valves convex 



2. Without external ribs but almost always with threads, ridges, 

 or rows of scales or vesicles ; shell very thin 

 3. With internal ribs (except (Parvamussium) davidsoni) 

 4. Without byssal sinus; auricles equal or nearly; convex- 

 ity slight Genus Propeamussium 



4. With byssal sinus; auricles equal; convexity slight 

 Subgenus Parvamussium 



3. Without internal ribs 



5. Posterior auricles well-defined; maximum height 10 

 mm (except incongruus : 14 mm) ; right valve with 

 concentric lamellae or ridges only, and usually flexed 

 ventrally ; ctenolium nearly always absent ; many species 

 opaque, a few translucent . . Genus Cyclopecten 



5. Posterior auricles poorly defined; their lateral margins 

 continuous with outlines of disks (except greenlandicus: 

 oblique) ; right valve without concentric lamellae or 

 ridges (except in vitreus), and never flexed ventrally; 

 ctenolium always present; all species translucent . . 



Subgenus Delectopecten 



2. With external ribs 



6. Ribbing concentric; result of undulations of disks; shell 



very thin Subgenus Hyalopecten 



6. Ribbing radial 



7. Left valve nodose; 9-15 ribs; hinge dentition pro- 

 nounced and strong diagonal crura adjoining resilial 

 pit Genus Nodipecten 



7. Left valve not nodose 



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