MARINE MOLLUSCA OF THE UNITED STATES. 19 



Shell minute, orbicular, depressed, few-whorled ; peristome continuous, 

 entire, round ; operculum paucispiral. Srenea, Fleming. 



Shell minute, discoidal, convex above, concave beneath, umbilicated ; sur- 

 face glossy ; operculum thin, flexible, pellucid. 



Cochliolepis, Stimpson. 



Genus LITTORINA, Ferussac. 



The periwinkles are found on the sea-shore in all parts of the 

 world ; they can exist for a lengthened period out of water, and 

 usually inhabit situations which are only covered by the sea at 

 high tide. The species are numerous, and the genus is represented 

 in all parts of the world. 



1. L. dilatata, d'Orbigny. Fig. 144. 



Moll. Cuba, 207, t. 14, f. 20-23. 



Shell subpyramidally conical, rather thick, imperforated, livid- 

 gray, encircled with white nodules; whorls slanting at the upper 

 part; columella broadly concavely dilated, purplish-brown. 



Chiefly remarkable for the broadly excavated purple-brown 

 columella, and conspicuous white nodules upon a livid-gray ground. 



Beaufort, North Carolina to West Indies. 



2. L. rudis, Donovan. Fig. 145. 



• (Turbo.) Brit. Shells, i. t. 33, f. 3. 1800. 

 T. obligatus, Say, Journ. Philad. Acad., ii. 241. 1822. 



Shell very strong and coarse, subovate, ventricose ; whorls five 

 to six, convex, tapering rapidly to a little elevated spire, and 

 covered with revolving elevated lines and grooves; body-whorl 

 with ten to twelve revolving costre, the intervening spaces finely 

 reticulated; lip plaited by the termination of the costre ; about 

 four of these on the next whorl, and obsolete above; base of the 

 lip broadly bevelled ; pillar-margin also broadly flattened ; aper- 

 ture regularly oval; color obscurely brownish, sometimes orange 

 or olive, occasionally banded with white. 



Length 12.5 mill. 



New England and Middle States (N. Enrobe). 



3. L. tenebrosa, Montagu. Fig. 146. 



{Turbo.) Test. Brit., 303, t. 20, f. 4. 1803. 

 T. restitus, Say, Journ. Philad. Acad., ii. 241. 1822. 

 L. rudis (part), Stimpson, Shells N. E., 33. 1851. 



Shell small, conic, not as stout as rudis; spire elevated and 

 pointed, as long as the aperture ; whorls five to six, rounded, with 



