TRIFORIS. 323 



tened, traversed by numerous folds or ridges, of which there are 

 from twenty to twenty-five on the lower whorl, crossed by three 

 revolving impressed lines, producing three series of gran- ^.^^ ,^^ 

 ulcs, of which the lower one is largest, so that the base of 

 each whorl seems to jut over the one below it ; the upper 

 series is nearer to the middle one than that is to the lower 

 one, and soon disappears on the upper whorls ; then the 

 middle one vanishes, and finally the lower one, so that the 

 whorls at the apex are either smooth or merely wrinlcled ; 

 two black threads, emerging from the aperture, revolve around the 

 base of the shell ; suture distinctly marked ; aperture about one 

 eighth the length of the shell, nearly circular, terminating in a deep, 

 very short canal, partly closed over by the lips ; outer lip sharp, 

 notclied, and a little everted ; pillar twisted, regularly arched above. 

 Length, one fiftli of an inch ; breadth, one twentieth of an inch ; 

 divergence, thirty-five degrees. 



Found hy Professor Adams in Dartmouth Harbor, clinging to 

 marine plants, a few feet below low water, with other species. Bos- 

 ton Harbor, southwards (^Stimpsoii). 



This little shell would hardly be distinguished when mixed with 

 the young of B. nigrum. Its color is the same, and it is not unlike 

 it in marking. From the full-grown shell it is readily distinguished 

 by its bulging shape, the apparent jutting of one whorl over an- 

 other, its smaller size, and by its deeply notched canal. 



Genus TRIFORIS, Desh. 1825. 



Shell turreted, sinistral ; aperture round, produced anteriorly 

 into a closed, tubular canal, sometimes with a posterior, closed 

 canal. 



Triforis nigrocinctus. 



Fig. 182. 



Sliell small, reddish-black, granulated ; Avhorls twelve, reversed ; aperture 

 small ; beak short and recurved. 



Ceritliinm nirjrncinrliim, Adams, Bost. Journ. Nat. Hist. ii. 286, pi. 4, fig. 11. — Gould, 



Inv. 1st ed. 277, fig. 182. 

 Triforis nigrocinctus, Stimpson, Check Lists, ."). 



Shell small, conico-cylindrical, blackisli-red, with three revolving 

 series of rounded, bead-like granules, formed by numerous ribs or 



