A. E, Verrill —Mollusca of the New England Coast. 191 



In size, form, and the general character of the sculpture this spe- 

 cies resembles /8. formosa J., from which it differs mainly in the 

 more delicate character of the sculpture, less acute carinoe, finer and 

 closer ribiets, and much more numerous and finer lines on the base. 

 The typical form of jS. 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 S. carinata Jeff, and *S. ionica 

 Watson it differs in having a higher and more acute spire, and decid- 

 edl}^ 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 coriiinoduin Middendorff, Beit. Malacozoologia Rossica, pi. 17, figs. 4-11, 



1847. 

 f Pilidium radiatum M. Sars ; G. 0. Sars, Moll. Reg. Arct. Norvegiaj, p. 144, pi. 8, 



figs. 6, a-d, pi. V, figs. I, a,h (dentition). 

 Pilidium commodum Friele, Nyt. Mag. Naturvid,, xxiii, 1877, [sep. copy, p. 2], pi., 



figs. 2, 2a, dentition. 



Shell very thin, translucent, bonnet-shaped, with the antei'ior 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 covei'ed with rather conspicuous, close, raised lines of 

 growth, but is destitute of any i-adiating 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 corx-esponds 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 



