24 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 23 



Gyclopecten benthalis sp. nov- 

 Plate 5 



Shell quite small, translucent, very slightly higher than long, and 

 equivalve; hinge line about half as long as disk and beaks protruding 

 slightly. Right valve flatly convex, with reflexed ventral margin (about 

 % total height of valve) ; numerous faint concentric ridges and, along 

 ventral margin, numerous even fainter radial ridges. Anterior auricle 

 longer than posterior, concentrically lamellose and with 3 distinct radial 

 ridges; byssal notch shallow and no ctenolium. Posterior auricle small, 

 with perpendicular margin and covered by fine concentric lamellae. 

 Left valve moderately convex and radially corrugated, resulting in 13 

 low primary ridges with a few irregularly disposed secondary ridges 

 between some of them, 9 secondary ridges adjoining anterior submargin 

 and 7 adjoining posterior; minute subglobular vesicles on primary ridges, 

 about 1/2 mni apart. Auricles of same size as corresponding ones of right 

 valve; both with fine concentric lamellae and 6 very faint radial ridges. 



Holotype: Height 8 mm; length 7.5 mm; diameter 1.75 mm; hinge 

 line 3.9 mm; only specimen known. Allan Hancock Foundation. 



Type locality: 14.5 miles NNW of San Nicolas Island, California, 

 in 490 fathoms, gray-green mud, tubiculous annelids, foraminiferans, 

 Phyllochaetopterus sp. ; Hancock station 3031-55; 33°28'04"N, 

 119°34'41"W;May7, 1955. 



Remarks: Although it is seldom advisable to describe a new species 

 on the basis of a single specimen, the author feels justified in this in- 

 stance. 



The short hinge line and the ridges and sculpture of the left valve 

 distinguish this species from any other Pacific Gyclopecten. In general 

 aspect it resembles the Atlantic C. imbrifer (Loven) (1847, p. 185), 

 but that species differs in having larger anterior auricles with more 

 numerous radial ridges, imbricated posterior auricles, no fine radial 

 ridges on the right valve and more numerous and more profusely sculp- 

 tured radial ridges on the left valve. 



Gyclopecten subhyalinus (E. A. Smith) 1885 



Plate 6 



Pecten subhyalinus E, A. Smith, 1885, p. 304, pi. 22, figs. 2, 2a. [Off 



southern Chile.] 

 Gyclopecten subhyalinus (Smith). Verrill, 1897, p. 71; Antarctic. 

 Holotype: British Museum. 



