324 pyramidellidjE. 



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



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

 the upper series is smaller than the lower, at last disappear- 

 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 



r. n/^ro- place, and forms the lower edge of the last whorls; this 



cinctus 



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 about 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 lip sharp, notched by the re- 

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

 projecting. Length, three tenths of an inch ; lu'cadth, 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 Murex advei'sus, 

 Montagu, but is probably different, 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 appellation, on this account, is not well chosen. In some 

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



Family PYRAMID ELLID.^, Cieay. 



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

 front ; columella plaited. 



Genus ODOSTOMIA, 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. 



