Descriptions of some Shells, &c. 351 
ed, sharp; above, originating behind the axis of the shell, and rising 
a little higher than the shoulder: left margin, above, a thin plate 
glued upon the convexity of the second whirl, below, thickened 
and formed into a stout and glossy pillar which is twisted on the ax- 
is of the shell: an oblique fold exists at the junction of this pillar 
with the convexity of the whirl, and, as the pillar does not reach 
the base of the shell, its somewhat abrupt truncation has the ap- 
pearance of an obtuse tooth: umbilicus none: an interior callus 
strengthens the junction of the right lip with the top of the shell, 
and, from the greater opacity of this portion, seems to strengthen the 
whole interior of the shoulder ridge. 
Length, 0.15 of an inch. 
Breadth, 0.10 do. 
Inhabits muddy bottom in Newport harbor, (R. I.) Dredged 
from a depth of fifteen feet. 
Genus Natica, Adanson. 
N. immaculata. Fig. 6, a, 6, ¢. 
Shell, small, milk-white, immaculate, glossy, longitudinally sub- 
oval: volutions, about five: suture, not impressed: upper whirls, 
very slightly convex: umbilicus, rounded, scarcely modified by the 
callus: callus, not very copious, and, entering the aperture under 
the upper part of the right lip, runs to the apex, causing a white 
spiral line to appear on the exterior surface, just under the sutures : 
aperture, rather narrow, regularly and somewhat acutely curved at 
the base: operculum, horny. 
Length, 0.28 of an inch. 
Breadth, 0.22 = do. 
It probably attains a somewhat greater size. 
Inhabits Newport harbor, (R. I.) Dredged from deep water. 
This shell, in form, much resembles Say’s N. triseriata, (Jour. of 
Acad. of Nat. Sciences, Phil. Vol. v, p. 209) and is found associa- 
ted with it. It is distinguishable from that species, however, not 
only by the broad difference of color, but by the lesser convexity of 
the upper whirls, and by the aperture, which is narrower near the 
base, and not sub-angular at the bottom of the pillar, and also by 
the operculum, which, is more elongate and has a smaller spire. 
Fig. 6, 6 is the operculum of triseriata, and c that of the immac- 
ulata. 
& 
el tib onys hye allan 
