158 PROCEEDINGS OF THE NATIONAL MUSEUM vol. i09 



Cape, and south to Nunivak Island, the Aleutians, and Puget Sound; 

 about 6 specimens (including the figured type) from the Shetlands, 

 the British Isles, and Norway; and about 85 specimens from Green- 

 land, Labrador, Maine, and south to Cape Hatteras. 



Discussion: The young of this species are olive green to brown and 

 occasionally creamy tan; larger specimens vary from olive green to 

 brown to black, with various mixtures of these colors — for instance, 

 the center may be black and the anterior and posterior ends brown. 

 There is some variation in the coarseness of the striae. The shells 

 also vary in breadth from thin to relatively obese, the latter giving 

 rise to Dall's M. niger obesus. There are all intergradations between 

 the thin and the obese. In specimens from northwest Greenland, 

 Grand Manan, Long Island Sound, and Isle au Haut, Maine, there 

 are both thin and obese shells. Specimens from the north end of 

 Nunivak Island vary from medium thin to obese. 



A specimen 66 mm. in length from the north of Unimak Island has 

 about 13 growth cessation lines, plus several secondary lines, one 37 

 mm. in length has from 7 to 9 growth cessation lines; and 2 specimens 

 from west of the Colville River, measuring 49 mm. and 56 mm. in 

 length, have 11 and 15 lines, respectively. 



Distribution: Throughout the Ai-ctic; in the Pacific south to 

 Oregon; in the Atlantic south to Cape Hatteras, N. C, and to Scotland. 



Musculus corrugatus (Stimpson, 1851) 



Plate 4, figure 11; Plate 18, figure 7; Plate 21, figure 4 



Mytilus corrugatus Stimpson, 1851, p. 12 [no description but " = Modiola discors 



Gould"]. 



Modiolaria corrugata G. Sars, 1878, p. 30, pi. 19, figs. 2a-b. — Jensen, 1912, p. 62, 



pi. 3, figs. 7a-d. 



About 40 specimens, mostly small, were dredged: 1 (17.8 by 10.9 

 by 6.9 mm.) from Eluitkak Pass on Aug. 1, 1950; 3 (4, 4.5, and 13.8 

 mm. long) from 130 feet on Aug. 9, 1949; 2 (5 and 12.7 mm.) from 184 

 feet; 1 (7.3 mm.) from 204 feet (pi. 4, fig. 11); 2 (8.6 and 12 mm.) from 

 213 feet; 2 (6 and 6.5 mm.) from 216 feet; 6 (from 3.5 to 10.5 mm.) 

 from 217 feet; 2 (8.6 and 13.2 mm.) from 295 feet; 1 (13 mm.) from 

 341 feet; 17 (from 3.5 to 14.2 mm.) from 420 feet; 1 (13 mm.) from 

 438 feet; and 3 (5.8, 10.5, and 14.5 mm.) from 741 feet. 



Other material examined: 4 specimens from "north of Bering 

 Strait," 2 from Bernard Harbor, 3 from Dolphin and Union Straits. 



Discussion: The Point Barrow specimens vary in color, from a 

 very pale greenish to an olive green, in the degree of inflation, and in 

 the extent to which the basal margin of the posterior striated portion 

 projects below the unstriated middle portion (pi. 18, fig. 7). There 



