TURBINACEA. MOLLUSCA. ODOSTOMIA. 271 



State Coll., No. 29. Soc. Cab., No. 2373. 



Py'ramis fusca, Adams ; Bost. Journ. A''ut. Hist., ii. 282, pi. 4, f. 9. 

 Jaminia fusca, Adams ; Ibid., iii. 337. 



Shell small, thin, elongated-conical, rather blunt, or worn off 

 at apex, a smooth and glossy violet-brown epidermis covering it, 

 through which the lines of growth are perceptible ; whorls six, 

 probably eight when the tip is entire ; slightly convex, regulaily 

 tapering, and separated by a well-defined suture, and sometimes by 

 a revolving line just below it, so that the suture seems double ; 

 aperture ovate, widened at the middle by a twist of the pillar lip, 

 acutely angular behind ; simple and sharp, widely and regularly 

 rounded in front ; it ascends upon the columella, and forms an ob- 

 lique, nearly transverse ridge, as it revolves within the aperture, 

 and so deep as to be nearly concealed ; space between this fold 

 and the posterior angle of the aperture joined by a thin plate of 

 enamel ; an umbilical indentation about the middle of the left lip. 

 Length 2V inch, breadth j\ inch, divergence 26^. 



This shell was first found by Professor C. B. Adams, at New 

 Bedford, clinging to planks, not far above low-water mark, and 

 from him I received my specimens. They have since been found 

 at Dartmouth and Tiverton. 



Compared with O. exigua, with wliich shell it is most likely to be 

 confounded, it is shorter and more blunt-pointed ; the whorls are 

 more flat, and the lowest in exact keeping with the rest ; the color 

 very much darker ; the aperture is broader and modified by the twist 

 of the lefl margin, without any prolongation at base. The turning of 

 the hp into the aperture forms a fold, which, in some specimens, is not 

 seen without looking far within ; in others it is quite conspicuous, and 

 in others it is even divided by a furrow into two folds. The figure and 

 description in the " Boston Journal of Natural History " were drawn 

 from specimens much smaller and less perfect, than some since 

 found ; so that they are both imperfect. The spiral ridge or fold on 

 the columella is there said not to exist at all. 



These two last shells ditFer in some characters from the followino-, 

 and perhaps belong to a different genus. The shell is thin and horny, 

 the aperture regularly rounded in front, and the fold on the pillar in- 

 conspicuous. In the true Odosto'mi^, the shells are of a solid, ivory 

 structure, and the lip somewhat produced in front, forming the con- 

 necting link with Ceri'thium and the Canali'fera. 



