NO. 2183. NEW NORTHWEST AMERICAN BIVALVE8—DALL. 405 



Station 3197, off San Luis Obispo Bay, in 77 fathoms. 



None of the Pacific specimens have the golden yellow color of the 

 Atlantic species and none of them attaua the same size. Otherwise 

 the shells are very similar. 



DACRYDroM PACIFICUM, new species. 



Shell minute, whitish, much the shape of Musculus vernicosus Mid- 

 dendorff, on a mmute scale, differing from the Atlantic D. vitreum by 

 its smaller size and more elongated outline. Length, 3.6 ; height, 2.5 ; 

 diameter, 1.5 mm. Cat. No. 214092, U.S.N.M. 



Station 3604, 1,401 fathoms, mud, in Bering Sea. 



MUSCULUS NIGER Gray, new variety, OBESUS. 



Shell resembling the typical flattish form but markedly more 

 inflated. Length, 60; height, 31; diameter, 18 mm. Cat. No. 

 223317, U.S.N.M. 



Plover Bay near Bermg Strait, in 8 to 20 fathoms. 



MUSCULUS NIGER Gray, new variety, PROTRACTUS, 



Shell resembling the young of the typical form but more inflated 

 and elongated, the sculpture very distinct, the medial area smooth, 

 blackish, the dorsal areas ohvaceous. Length, 13; height, 6.5; 

 diameter, 5.5 mm. Cat. No. 222017, U.S.N.M. 



North of Nunivak Island, Bering Sea, in 9 fathoms, gravel. 



MUSCULUS OLIVACEUS, new species. 



Shell small, thin, pohshed, pale ohvaceous near the beaks, growing 

 darker distaUy; medial area smooth, anterior area with six or seven 

 rather strong radial grooves; posterior area with numerous shallow 

 channeled radii crossed by rather regular shghtly elevated concentric 

 lines, givmg a silky luster to the surface; beaks inconspicuous, 

 inflated; dorsum arched, base nearly straight, both ends evenly 

 rounded, the posterior shghtly wider; interior whitish, the margin 

 crenulated by the sculpture, the beaks very close to the posterior end. 

 Length, 10; height, 6; diameter, 5 mm. Cat. No. 210790, U.S.N.M. 



Off Bermg Island, m 10 fathoms. 



This differs in sculpture, color, and proportions from the young of 

 M. laevigatus. 



Genus LITHOPHAGA Bolten, 1798. 



Section LABIS Ball, 1916. 



Type. — LithopTiaga attenuata Deshayes. 



The typical Lithopliaga has a clean outer surface; Diherus a divari- 

 cate plumose posterior incrustation ; Myoforceps, two crossed conical 

 projections; the present form has on each valve a semicylindrical 



