44 
MARINE SHELLS OF WEST COAST OF NORTH AMERICA 
four to five posterior hinge teeth, which are small and delicate, the two 
series separated by a short edentulus gap. When the periostracum is re¬ 
moved, the sculpture is not unlike that of L. jousseaumi, but more em¬ 
phatic, and the radii are distinctly punctate. The interior is faintly grooved 
and the ventral margin distinctly crenulate, or rather beaded. Length, 12; 
height, 10; diameter, 11 mm. (Dali.) 
Type in U. S. N. M., No. 122585. Type locality, Station off San 
Diego, California, in 822 fathoms. 
Range. Santa Barbara Islands to Coronado Islands. 
SECTION EMPLECONIA Dali, 1908. 
Limopsis vaginatus Dali, 1891. 
Plate 14, figs. 2, 3. 
Proc. U. S. N. M., 14:190 and 17; plate 25, figs. 3, 6, 7. 
Shell large, ovate, with a dense brown hirsute epidermis, under which 
the valve is polished, radiately and concentrically striated; margin simple, 
polished, central part of the valves striate radiately, the muscular scars 
bounded inwardly by a radial elevated ridge, most prominent behind the 
anterior scar. Hinge with ten anterior and five posterior teeth, separated 
by a gape, beaks little elevated, ligament wide, subtriangular and black; 
behind the hinge the cardinal margin is deeply folded in, forming when 
the valves are shut a long, very narrow pit more than one-fourth as deep 
as the whole width of the shell at right angles to that margin; this pit is 
also densely hirsute. The outline of the shell margin is thus made reni- 
form. Length of shell with epidermis, 34; height at right angles to the 
hinge line, 30; diameter, 12 mm. Length of pit, 16 and depth, 5.5 mm 
(Dali.) 
Type in U. S. N. M., No. 122547. Type locality, Station 3330, off 
the coast of Unalaska Island, Bering Sea, in 351 fathoms. 
Range. Bering Sea and Aleutian Islands. 
Genus ARCA Linnaeus, 1758. 
Shell equivalve or nearly so, thick, sub-quadrate, ventricose, strongly 
ribbed or cancellated; margins smooth or dentated, close or sinuated 
ventrally; hinge straight, teeth very numerous, transverse; umbones 
anterior, separated by a flat, lozenge-shaped ligamental area, with numer¬ 
ous cartilage grooves; pallial line simple; posterior adductor impression 
double; pedal scars 2, the posterior elongated. (Tryon. S. S. Conch.) 
Type. Area nocs Linn. 
Distribution. World wide, most abundant in warm seas. 
