74 
MARINE SHELLS OF WEST COAST OF NORTH AMERICA 
Genus MODIOLARIA Beck (Jeffreys, 1863). 
Shell rhomboidal, sculptured by two rows (one on each side) of striae 
which radiate from the beaks, leaving the middle portion smooth; beaks 
incurved; hinge mostly toothless, but sometimes crenulated; hinge plate 
finely notched. (Tryon. S. S. Conch.) 
Type. Mytilus discors Linnaeus. 
Distribution. Temperate and Arctic seas. 
Modiolaria nigra Gray, 1824. 
Plate 13, fig. 21, and plate 39, fig. 9. 
App. Parry’s Voy., p. 244. Voy. de la Recherche; pi. 17, fig. 1. 
Shell oval, inclining to oblong, compressed, rather thin, moderately 
glossy and slightly iridescent; sculpture, about a dozen remote ribs on 
the anterior side, and 50 to 60 close-set and thread-like ribs on the other 
side, which latter become finer toward the middle of the shell; ventral area 
not depressed, but without ribs; transverse striae numerous, coarse and 
flexuous, sometimes forming tubercles or a rough network where they 
intersect the longitudinal ribs; colour purplish brown; epidermis rather 
thick, fawn colour in the young, olive green at a subsequent stage of 
growth, and dark brown or even pitch blade in aged examples; margins 
rounded on all sides except the ventral, which is nearly straight; beaks 
small, prominent, incurved, and diverging, placed at some distance from 
the anterior margin; byssal sinus, ligament and hinge line as in the other 
species; hinge plate strengthened by a rib to receive the ligament, and 
finely notched; ligamental groove narrow and deep; hinge crenulated; 
inside highly nacreous, purplish brown, finely notched on the anterior 
and posterior edges, and showing the impressions of the ribs as well as 
faint traces of similar but finer striae on the middle area; scars distinct. 
Length, 1.5; height, 0.65 inches. (Jeffreys, British Conchology.) 
Type in British Museum. Type locality, Orsund Bay, Sweden. 
Range. Arctic Ocean to Oregon. Circumboreal. 
Modiolaria nigra obesa Dali, 1916. 
Proc. U. S. N. M., 52:405. 
Shell resembling the typical flattish form but markedly more inflated. 
Length, 60; height, 31; diameter, 18 mm. (Dali.) 
Type in U. S. N. M., No. 223317. Type locality, Plover Bay, near 
Bering Strait, in 8 to 20 fathoms. 
Range. Arctic Ocean to Cape Flattery. 
