330 PYRAMIDELLIDiE. 



fifteen hundredths of an inch ; breadth, seven hundredths of an 

 hich ; divergence, tliirty degrees. 



First found by Professor Adams, at Dartmouth, on valves of 

 Pcctcii irradians, taken up beyond low-water mark. Massachusetts 

 Bay, northwards (^Sti/uj/soN). 



This shell is readily distinguished from all others found in our 

 waters of a similar size and outline, by tlie sculpture of the lower 

 whorl, the upper half of which is granulated by the decussating 

 lines, and the lower half marked by revolving lines only. It is 

 smaller, and less elevated proportionally than O. trijida. Making 

 allowance for variations in magnifying two shells so small, this 

 seems not to diifer much from Turbo spiralis of Montagu (Test. 

 Brit. 323, pi. 12, fig. 9). Ho neither represents nor describes any 

 revolving lines crossing the folds ; but they might possibly have 

 been overlooked, for Fleming distinctly mentions them. 



[Animal, eyes large, black ; when in the water it often hangs by 

 a mucous thread from the surface, which is attached to the posterior 

 part of the foot ; gregarious. 



Odostomia impressa. 



Titrritclla imprcssn, Say, Joiirn. Ac. Nat. Sc. ii. 244 (1822) ; ed. Binney, 84. 



Odostomia impressa, Stimpson, Check Lists, .5. 



Odostomia insculpta, De Kay, N. Y. Moll. 115, pi. 31, fig-. 297. 



Fig. 600. Shell dusky, acute at the apex ; volutions six, with about 

 four acute, impressed, revolving lines; labrum not thickened, 

 a slight indentation at its base, and a projecting angle within 

 its middle. 



Inhabits the coast of Maryland. Length, more than an 

 eighth of an inch. 



I have seen but two specimens of this species. The aper- 

 ture is precisely similar to that of the preceding species, T. altcr- 

 nata. (Sa//). 



Connecticut ( Slimpsun). 



Genus TlTRBONILL,A, Leach. 1825. 



Shell slender, elongated, many whorled, longitudinally ribbed ; 

 apex of spire with persistent, embryonic, sinistral nucleus ; aperture 

 oblong or sub-quadrate, peristome incomi)lete ; columella straight, 

 simple, edentulatc, and without a plait. 



