40 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 23 



Key to the eastern Pacific Species of Delectopecten 



1. Shell quite oblique; disks either smooth or with very fine (occa- 

 sionally scaly) radial threads and minute concentric incremental 

 lines; specimens higher than 10-14 mm, having ctenolium of 



minute beads zacae (Hertlein) 



(Galapagos Islands; Gulf of Panama to northern Gulf of 

 California) 



1. Shell not oblique, or only very slightly; disks often obscurely un- 

 dulated ; ctenolium of 3-6 teeth 

 2. Disks either smooth or with very minute radial striae 



randolphi (Dall) 



(Bering Sea to Guaymas, Mexico, in Gulf of California) 

 2. Disks variously sculptured 



3. With spines or scales 



4. With spinose radial ridges and finer concentric ridges ; 

 interior of posterior auricle of right valve with angulate 

 ridge . . . randolphi tillamookensis (Arnold) 



(Bering Sea to Cedros Island, Lower California) 

 4. With 60 or more finely spinose radial ridges but no con- 

 centric ridges . . . vancouverensis (Whiteaves) 

 (Bering Sea to southern end of Lower California; Gulf 

 of California north to San Ildefonso Island) 

 4, With about 36 radial rows of scales; fairly prominent 

 low and smooth radial ridges covering disk 



polyleptus (Dall) 



(Of? southern Chile; Galapagos Islands) 

 3. With concentric rows of vesicles, connected to each other 

 by fine concentric ridges; also minute divergent radial 



striae vitreus (Gmelin) 



(Strait of Magellan and off southern Chile; Clipperton 

 Island; for complete range see species, this paper) 



Gyclopecten (Delectopecten) vancouverensis (Whiteaves) 1893 



Plate 15 



[raora] Pecten caurinus Gould. Dall, 1886, p. 216, pi. 5, fig. 4. ". . . 

 young specimen . . . Sitka, Alaska." [ = vancouverensis Whit- 

 eaves.] 



