38 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 23 



At the author's request Dr. Harald A. Rehder, of the U. S. National 

 Museum, compared individuals of this species with the holotype of 

 Dall's Pecten incongruum; his comments follow: "The specimens from 

 off Santa Barbara Island are not P. incongruum Dall, which is quite 

 different, larger, flatter, and with the axial riblets not as strong, so that 

 the sculpture is not as fenestrated as in your species. The concentric 

 riblets of the latter are much more lamellate than in incongruum^ 

 Dall's species also differs from Cyclopecten barbarcnsis in being thicker 

 and opaque, rather than thin and nearly translucent. 



The recorded depths are quite shallow, but this species undoubtedly 

 also lives in considerably deeper water. 



Subgenus DELECTOPECTEN Stewart 1930 



Delectopecten Stewart, 1930, p. 118. [Proposed as a subgenus of Pallio- 

 /mw.] Type species: Pecten (Pseudamusium) vancouverensis 

 Whiteaves, 1893, p. 133, pi. 1, figs. 1-la; type locality: Forward 

 Inlet, Quatsino Sound, Vancouver Island, British Columbia, Can- 

 ada, in ten to twenty fathoms, mud. [For geographical range see 

 Cyclopecten (Delectopecten) vancouverensis, this paper. Whiteaves, 

 Dall and several other authors invalidly emended Pseudamussium 

 to Pseuda??iusium.] 

 Arctinula Thiele, 1934, p. 806. [Proposed as a section of Palliolum.] 

 Type species: Pecten Greenlandicus Sowerby, 1842, p. 57, pi. 13, 

 fig. 40; type locality: Greenland. 

 Catillopecten Iredale, 1939, p. 370. Type species: Pecten murrayi E. A. 

 Smith, 1885, p. 303, pi. 22, figs. 1-la; type locality: Challenger 

 station 184, east of Cape York, Queensland, Australia, in 1400 

 fathoms. 

 Original diagnosis: In not having the posterior ear differentiated, 

 Delectopecten includes a group of small forms now living in the N. E. 

 Pacific which have been classed as "Pseuda/nussium" by Dall . . ., 

 "Pecten' murrayi Smith from Australia . . ., and Palliolum vitreum .... 

 "Pecten (Pseudamussium)" polyleptus Dall, from the Galapagos Is- 

 lands and "P. (Pseudamusium)" panamensis Dall also belong to this 

 group .... [panamensis Dall, 1908; panamensis Dall, 1898 = zacae 

 Hertlein, 1935.] Palliolum vitreum, which is from the North Atlantic, 

 was apparently included in the original Palliolum Monterosato (1884, 

 p. 5-6), but ''Pecten" incornparabilis Risso, which has been designated 

 as type species of Palliolum (Crosse, 1885, p. 140) seems to have a 

 distinct posterior ear .... The type species of Delectopecten is "Pecten 



