32 
MARINE SHELLS OF WEST COAST OF NORTH AMERICA 
Retusa semen Reeve, 1856 
Plate 2, fig. 13 
Belcher, Last of the Arctic Voyages, 2:393. 
B. semen Bui. testa cylindraceo-ovata, tumidiuscula, spira depresso- 
convexa, sutura impressa, anfractibus laevibus, convesiusculis, ultimo 
antice paululum descendente; fulvescente-alba. 
Of a short cylindrical form, somewhat swollen, with a depressly convex 
spire, having the suture faintly channeled. (Reeve.) 
Type locality, Port Refuge; Nova Zembla. 
Range. Off Point Collinson, Arctic; also Atlantic. 
Described as Retusa semen. 
Retusa obtusa Montagu, 1803 
Testacea Britannica, 1:223; PI. 7, fig. 3. 
With a moderately strong, subcylindric, opaque-white shell, wrinkled 
longitudinally; apex convoluted, obtuse; volutions four or five, very little 
produced; aperture nearly the whole length of the shell, narrow, rather 
more compressed in the middle, dilated at the base; inner lip thickened, 
smooth, white. Length rarely % in.; breadth, about half its length. 
(Montagu.) 
Type in? Type locality, England. 
Range. Arctic Ocean to St. Mathews Island. Circumboreal. 
Retusa pertenuis Mighels, 1843 
Boston Journal of Natural History, 4:346; PI. 16, fig. 3. 
Shell very small, cylindrical, of a dingy white color, very thin and 
fragile; whorls four, rounded, all lying in the same plane; suture distinct, 
as seen under the microscope; spire elevated; labrum nearly straight at 
the posterior part, rounded anteriorly, returning into the shell it forms a 
delicate, slightly elevated lamina, which, under the miscroscope, is seen 
to occupy nearly the whole length of the columella region; aperture very 
narrow posteriorly, broad and rounded anteriorly. Length, .08; breadth, 
.04 in. (Mighels.) 
Type is lost. Type locality, Casco Bay, Maine. 
Range. Arctic Ocean; Bering Sea; also Atlantic. 
Mighels’ types were placed in Museum, Portland, Maine, which was 
burned. 
[32] 
