324 PYRAMIDELLID^. 



folds, Avliicli are cut by two deep, revolving lines into equal parts ; 



the middle series is wanting on the posterior fifth of the shell, and 



the ui)ncr series is smaller than the lower, at last disappear- 



Fi" 592. '11 



ing also ; whorls twelve or more, reversed, convex, forming 

 an elongated, acutely pointed spire, somewhat swelling in 

 its outline ; suture broad, divided by a somewhat granular, 

 black ridge, which, in the progress of growth, changes its 

 place, and forms the lower edge of the last whorls ; this 

 ridge retains its color when the rest of the shell fades, and 

 then becomes a conspicuous belt ; an impressed line each side of 

 the sutural ridge, and two others emerging from the aperture, re- 

 volve al)0ut the base of the anterior whorl ; aperture oval, about one 

 fifth the length of the shell, ending in a twisted canal about one 

 third as long as the aperture ; outer lij) sharp, notched by the re- 

 volving lines ; inner lij) deeply arched, the pillar twisted, black, and 

 j)rojccting. Length, three tenths of an inch ; breadth, three forti- 

 eths of an inch ; divergence, twenty-three degrees. 



Found by Professor Adams, in Dartmouth Harbor, clinging to 

 sea-weed, a few feet below low-water mark. 



It is at once distinguished by its black color, slightly tinged red, 

 and its reversed whorls. It is closely allied to the Mtircx adi-ersiis, 

 Montagu, l)ut is probably ditferent, as that shell has the middle se- 

 ries smaller, and the canal straight. It is also of a lighter color. 



The whole shell, when fresh, is of a uniform color, so that the 

 dark revolving line at the suture is scarcely distinguishable, instead 

 of something evident, as we should expect from the name. The 

 specific ajipellation, on this account, is not well chosen. In some 

 lighter colored individuals, however, the zone is very apparent. 



Family PYRAMIDELLID^, Gray. 



Shell turreted ; aperture entire or not produced into a canal in 

 front ; columella plaited. 



Genus ODOSTOI?IIA, Fleming. 1828. 



Shell conical, elongated ; aperture ovate ; lips disunited poste- 

 riorly, and sometimes produced anteriorly ; pillar with a tooth-like 

 fold ; operculum horny, sub-spiral. 



