GASTEROPODS 371 



The littorinas fairly swarm in favorable localities upon all 

 shore stations. In Maine and Massachusetts the bold, rocky 

 coast furnishes a home for several species. Often the rocks at 

 low tide are black with them ; the algse that cling in wet masses 

 to the exposed rocks are alive with them. One cannot walk 

 about in such localities without crushing hundreds of specimens. 

 Sometimes they will be found clinging in clusters upon the piling 

 of old wharves, or crawling about the bottom at or about the low- 

 tide mark. The best specimens of Littorina are found in stations 

 where they are bathed twice a day by pure, uncontaminated sea- 

 water; those living near the mouths of streams, or where the 

 water is brackish or impure, are usually small and degenerate. 

 They are vegetable feeders, and have received the common name 

 of "periwinkles." In Great Britain they are used among the 

 poorer classes for food. The animal has a short, broad muzzle, 

 and eyes at the outer bases of the tentacles. The foot is longi- 

 tudinally grooved, and there is a rudimentary siphonal fold in the 

 mantle. The shells are turbinated, usually heavy, few-whorled, 

 and with a round aperture. 



L. litorea. This is supposed to be an importation from the Old 

 World to have come over by way of Iceland and Greenland, and then 

 to have migrated down the Labrador coast. For many 

 years Cape Cod formed a barrier to its advance, but 

 now the species is abundant at Newport, and is reported 

 at New York. It occurs on the Maine coast in astonish- 

 ing numbers, living in vast colonies on the rocks exposed 

 at low tide. The shell is thick, imperf orate (no umbil- 

 icus), and usually has flat, spiral ribs. The columella is 

 broad and white ; the lip thin and black. The general 

 color varies from black to olive or to dingy gray some- 



jj- i mi i -ii J.T Littonna litorea. 



times reddish. Ihe operculum is corneous, with the 

 nucleus near the outer edge. Despite the variableness of this very 

 common shell (the variations being chiefly in the height of the spire), 

 it has certain unmistakable characteristics which, once seen, 

 will enable the collector to determine it at once. 



L. rudis. A smaller species than the last. It is strong 

 and coarse, with revolving grooves and ribs, or smooth, with 

 interrupted whitish bands and spots. A very common vari- 

 ety of this species is much smaller than the typical form, 

 being about one sixth to one fourth of an inch long, smooth, 

 with white and yellowish spots on olive. It clings to the rocks 

 near high-tide mark, and is usually found attached to its 

 resting-place by a bit of hardened mucus. While the typical L. rudis 

 is heavy and banded, with a moderately high spire and no color, this 



