CANALIFERA. MOLLUSCA. CERITHlUM. 277 



This species is closely allied to C. Emersonii. Its size and pro- 

 portions are the same ; but it can scarcely be regarded as a variety. 

 It is at once known by the prominent ridges, which resemble the 

 threads of a screw. There is nothing like the nodulous surface of 

 C. Emersonii, and the minute barring between the ridges is a striking 

 arrangement, to which there is no approach in that shell. 



NIGROCI'NCTUM. 



Shell small, reddish-black, granulated ; whorls twelve, reversed ; 

 aperture small ; beak short and recurved. 



FIGURE 182. 

 State Coll., No. 279. Soc. Cab., No. 2363. 



Cerithium nigrocinctum, ADAMS ; Bost. Journ. Nat. Hist., ii. 286, pi. 4, f. 11. 



Shell small, conico-cylindrical, blackish-red, with three revolv- 

 ing series of rounded, bead-like granules, formed by numerous 

 ribs or folds, which are cut by two deep, revolving lines into 

 equal parts ; the middle series is wanting on the posterior fifth of 

 the shell, and the upper series is smaller than the lower, at last 

 disappearing 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 

 c^lor when the rest of tbe shell fades, and then becomes a con- 

 spicuous belt ; an impressed line each side of the sutural ridge, 

 and two others emerging from the aperture, revolve 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 revolving lines ; inner 

 lip deeply arched, the pillar twisted, black and projecting. 

 Length -$ inch, breadth ^ inch, divergence 23. 



Found by Professor Adams, in Dartmouth harbour, 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 advirsus, Mon- 



