A, EF. Verrill —Mollusca of the New England Coast. 191 
In size, form, and the general character of the sculpture this spe- 
cies resembles S. formosa J., from which it differs mainly in the 
more delicate character of the sculpture, less acute carinze, finer and 
closer riblets, and much more numerous and finer lines on the base. 
The typical form of S. formosa is destitute of an umbilicus, although 
a narrow one appears in some of the small specimens. This species 
seems to be a thinner and more delicate shell than any of the varie- 
ties of S. formosa, and has a more convex base and a smaller 
nucleus, but a less acute spire. From 8S. carinata Jeff. and S. tonica 
Watson it differs in having a higher and more acute spire, and decid- 
edly in the sculpture and the narrowness of the umbilicus, which in 
this form is a deep, narrow, spiral perforation. I have seen no de- 
scription of S. elegans Jeff, other than the statement that it is 
umbilicated. 
Piliscus commodus (Middendorff.) 
Pilidium commodum Middendorff, Beit. Malacozoologia Rossica, pl. 17, figs. 4-11, 
1847. 
? Pilidium radiatum M. Sars; G. O. Sars, Moll. Reg. Arct. Norvegize, p. 144, pl. 8, 
figs. 6, a-d, pl. v, figs. 1, a, b (dentition). 
Pilidium commodum Friele, Nyt. Mag. Naturvid., xxiii, 1877, [sep. copy, p. 2], pl., 
figs. 2, 2a, dentition. 
Shell very thin, translucent, bonnet-shaped, with the anterior slope 
rising gradually to the apex, which recurves and overhangs the 
posterior margin. Aperture very large, broad-ovate, a little nar- 
rowed posteriorly, broadly rounded in front. Apex prominent, situ- 
ated near the posterior end, curved backward and inward, and 
twisted obliquely to the right; the extreme apex is rather large, 
bluntly rounded, incurved, and appressed against the body of the 
shell posteriorly; this nuclear portion expands at first only grad- 
ually, and appears to be minutely punctate under a lens. The body 
of the shell is covered with rather conspicuous, close, raised lines of 
growth, but is destitute of any radiating lines. The whole surface, 
except the apex, is covered with a thin, fibrous, concentrically corru- 
gated, yellowish white epidermis, which easily peels off when dried. 
Margin very thin and sharp, flaring, especially in front. Internally 
the cavity of the shell corresponds closely with the exterior form, the 
apical portion running up into the nucleus of the shell and becoming 
subspiral. Muscular scars very indistinct. Posterior slope abrupt, 
almost perpendicular, and somewhat concave in a side view, and 
overarched by the projecting apex, which is situated rather to the 
