276 INVERTEBRATA OF MASSACHUSETTS. 



sent Mr. Sowerby a poor representation of our shell, or that he would 

 decide differently on a second, more careful inspection. No author 

 ascribes to M. tuherculdris more than eight or ten volutions, and one 

 fourth of an inch for its length ; while ours has commonly twice that 

 length, with sixteen or eighteen volutions. Montagu says, in his Sup- 

 plement, " It has as an invariable character, three series of tubercles 

 of equal size, on each volution." But at the ordinary length of M. 

 tuherculdris, our shell has but two series of granules ; and when the 

 third appears, it is very perceptibly smaller than the other two series. 

 On account of so decided a variation in size and sculpture, I think it 

 proper stdl to regard our shell as a distinct species, trusting to future 

 observations to settle the point definitely. 



Ceri'thium terebrale. 



Shell conic-turreted ; whorls ten, Jlattened, having three sharp, 

 elevated, revolving ridges on each, with numerous fine, longitudinal 

 lines between the ridges ; canal very short. 



Figure 181. 



State Coll., No. 280. Soc. Cab., No. 2364. 



Cerithium terebrale, Adams ; Bosi- Journ. JVat. Hist., iii. pi. 3, f. 7. 



Shell small, elongated-conic, composed of ten or twelve flatten- 

 ed whorls, separated by a slightly excavated sutural region ; color 

 reddish-brown, with occasionally a whitish revolving band at the 

 lower part of each whorl. On each whorl are three elevated, 

 compressed, revolving ridges, at about equal distances from each 

 other, and perhaps we may reckon a fourth, very small and bor- 

 dering on the suture. The spaces between the ridges are regu- 

 larly rounded out, and checked with crowded, minute, longitudinal 

 lines, none of which cross the summits of the ridges. On the 

 lower whorl are two additional ridges. The base of the shell is 

 abrupt ; the canal very short and small ; the aperture oval, about 

 one eighth the length of the shell. Length | inch, breadth 

 •J inch, divergence 20°. 



Found by Mr. C. F. Shiverick, at New Bedford and in its 

 vicinity, below low-water mark. 



