MARINE MOLLUSKS — MACGINITIE 127 



from 184 feet; 1 (15.7 by 7.1 mm.) from 341 feet; and 2 (44.6 by 17.6 

 mm., and 52.7 by 22 mm.) from 420 feet. The largest specimen is 

 a dead shell, measm'ing 69.3 mm. in height, from 150 feet. 



Some of the living shells had the usual quota of foraminifers and 

 small barnacles, and in several there were large areas covered with 

 colonies of bryozoans. 



Other material examined. — Three specimens from Point Barrow 

 and the "Arctic Ocean," several specimens (labeled P. verkruzeni) 

 from Icy Cape, Cape Prince of Wales, Bering Strait, Plover Bay, and 

 Queen Charlotte Sound, British Columbia; about 25 specimens from 

 the Grand Banks, Green Bank, Labrador, and the Gulf of St. Lawrence. 



Discussion: The greatest variations in the specimens from Point 

 Barrow, as well as in those from other locahties, are in the strength 

 of the axial ribs (see pi. 10, figs. 11-13), which range from those that 

 are practically obsolete through medium to stout, and in the propor- 

 tion of the length of the aperture to the remainder of the shell. The 

 latter variation is shown in table 3. The 2 specimens from 341 feet 

 have only weak folds near the sutures (as in Tryon and Pilsbry, vol. 3, 

 pi. 53, fig. 336); the dead shell from 150 feet has prominent, stout ribs 

 (loc. cit., pi. 53, fig. 335); others have ribs that are intermediate in 

 strength (loc. cit., pi, 53, fig. 334); and still others may have stout, 

 prominent ribs on the apical whorls and only faint ones on the body 

 whorl. Some shells are twice as thick or heavy as others of comparable 

 size. The throat varies from a deep buff to white faintly tinged with 

 Hght buff. 



Several of the Point Barrow specimens correspond with those that 

 Dall identified as P. verkruzeni (Kobeit). However, Dr. Thorson, 

 who examined about half of them on his recent visit to the West Coast, 

 says that they correspond fully with varieties of P. kroyeri in the 

 Danish collections from Greenland, and Tryon and Pilsbry illustrate 

 a relatively smooth form of P. kroyeri. In his description of P. 

 verkruzeni, Kobeit speaks of an ovately turreted, ahnost smooth 

 shell, with a very short, soUd canal. His description was based on 

 two specunens brought back by Verla-uzen from Porsangen Fjord in 



Table 3. — Comparison of length of aperture and remainder of shell in specimens of 



Plicif usus kroyeri 



Shell 



1, Adult, with stout ribs 



2, Immature, with stout ribs 



3, Adult, with stout ribs on apical whorls, weak on 



last whorl 



4, Adult, smooth form with weak folds on apical 



whorls 



5, Similar to No. 4 



