224 
MARINE SHELLS OF WEST COAST OF NORTH AMERICA 
rence, off Newfoundland, off Halifax, off Nova Scotia, Gulf of Maine, 
George’s Banks, Atlantic. Seahorse Islands, Arctic. Bering Strait, St. 
Paul, and St. George, Islands, Puget Sound, and Astoria, Pacific. 
Genus FRIELEIA Dali, 1895. 
Shell resembling Hemithyris Orbigny, from which it is distinguished by 
having the inner upper margins of the crura extended toward each other 
and united to the upper edge of a rather prominent, median septum, form¬ 
ing a spondylium, and in having the branchia consisting of a much smaller 
number of coils. (Dali.) 
Type. Frieleia halli Dali. 
Distribution. West coast of North America. 
Frieleia halli Dali, 1895. 
Proc. U. S. N. M., 17 :714; pi. 24, figs. 6, 9-13. 
Shell of moderate size, thin, translucent, yellowish gray, dorsoventrally 
somewhat compressed, slightly impressed in the median line below, but the 
basal margin hardly, if at all, flexuous; surface smooth, polished, except 
for faint, irregular radial markings and delicate incremental lines, occa¬ 
sionally modified by accidents of growth; pedicle valve pointed above, 
rounded at the lower corners, with a sharp, short beak slightly recurved, 
below which is a nearly circular peduncular orifice, bounded below by 
two well-marked sub-triangular deltidial plates, which do not quite meet 
in the median line; cardinal margin below them evenly arched and passing 
without an angle into the lateral margins of the valve, which for some 
distance are almost straight; the margins then round evenly into the base, 
which in many specimens is nearly straight, in others slightly excavated 
mesially; the margins are almost entirely in one vertical plane; teeth much 
as in Hemithyris psittacea, short, stout, projecting at right angles to the 
plane of the valve margins, and slightly recurved below; supported by 
slender buttresses which rise from the valve and extend upward into the 
cavity of the beak, leaving narrow recesses between the buttress and the 
side of the valve; in the interior of the beak there is no mesial septum, and 
the thinness and translucency of the polished valve are such that hardly 
any trace of muscular impressions is left on the shell; these impressions, 
if visible, would extend only three-fourteenths of the distance from the 
cardinal margin toward the base of the valve, while in H. psittacea the 
proportion is about eight twenty-firsts; the interior of the valve under 
moderate magnification shows with great clearness the reticulated outlines 
of the prisms of shelly matter forming the internal layer of the shell, but 
there are no other internal markings; brachial valve hardly less inflated 
than the other, roundly pointed above, with a well-defined, slender, sharp- 
