54 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 23 



Pseudamusium andersoni Dall, 1919, p. 19a, pi. 2, figs. 7, 8. "Station 

 43a, Canadian Arctic Expedition, off Cockburn Point, Dolphin and 

 Union Strait, Northwest Territories, Canada, in about 50 fathoms, 

 gray mud and stones." 

 [«o«] Pecten (Plagioctenium) andersoni Arnold, 1906, p. 82, pi. 26, 

 figs. 5, 5a, 6, 7, 8, 8a. Lower, middle, and probably upper Miocene 

 of California ; Miocene of Lower California. 

 Pecten (Pseudamusium) andersoni Dall. Dall, 1921, p. 20. Dolphin and 



Union Strait, Arctic Ocean. 

 Pecten bino?ntnatus Hanna, 1924, p. 175. "New name for P. (Pseud- 

 amusium) andersoni Dall, not P. (Plagiopecten) [jic] andersoni 

 Arnold." — La Rocque, 1953, p. 34. "Known only from the type 

 locality." 

 Palliolum groenlandicum (Sowerby). Soot-Ryen, 1932, p. 9. "Dall 

 (1919) describes Pseudamusium Andersoni . . . nearly related to 

 P. groenlandicum . . . perhaps only a variety . . . Not found [groen- 

 landicum] in the Pacific, the Chukotsk and the Beaufort Sea. 

 Occurring along the Eurasian shelf from 167° 30' E. and in the 

 Atlantic south to off Sudan and to the Gulf of St. Lawrence. Also 

 found to the north of America." 

 Palliolum (Arctinula) groenlandicum (Sowerby). Thiele, 1934, p. 806. 

 Pecten binominatus Hanna. Proc. Conch. Club So. Calif., 1944, no. 35, 

 p. 14a. ". . . unfigured species with the position something of a 

 mystery." 

 Holotype: ? 



Type locality : Greenland. 



Original description : T. aequivalvi, orbiculari, sub-compressa, sub- 

 aequilaterali, pellucida, tenuissima, laevi ; auriculis parvis, obtusangulatis, 

 anticis minoribus ; valva dextra lamina tenuissima, opaca, induta. Long. 

 1 ; lat. 0.25 ; alt. 1 ; poll. 



Additional description : The shell is rounded, inequivalved, very 

 thin, hyaline, nearly smooth, often with a violet iridescence when fresh. 

 The left valve is covered, even from the nucleus, with fine microscopic 

 camptonectes sculpture, in the form of thin, raised, divergent riblets, 

 more or less irregular and wavy, most visible by translucency. The left 

 valve sometimes has, also, fine radial striae and delicate lines of growth. 

 The margins are thin and smooth, that of the right valve turns up a 

 little against the other, which is larger, and the valves close very tightly, 

 so that anteriorly there is scarcely any visible gape, even at the byssal 

 notch or at the end of the auricle. The byssal notch is well-marked and 



