LITTORINA. 305 



color, but occasionally banded with white, or blotched with some 

 lighter color ; surface marked with very perceptible and sometimes 

 conspicuous revolving lines and grooves ; whorls four or five, con- 

 vex, well defined by the suture, forming a moderately ele- ^..^ ^.^ 

 vated spire, rather obtuse at its apex ; last whorl three 

 fourths the length of the shell ; aperture one half the same, 

 obliquely broad-ovate ; outer lip bevelled within to a sharp 

 edge ; the pillar margin is broadly flattened, and, widening 

 forwards, projects so as to form an angle ; within colored, 

 generally brown, except the bevelled edge, which is yellowish-white ; 

 operculum horny, sul>spiral ; sometimes a small umljilical indenta- 

 tion is found. Length, one half inch ; breadth, two fifths of an 

 inch ; divergence, sixty-eight degrees. 



Found on rocks of the ocean shore. Prince Edward's Island, 

 Labrador, Newfoundland (^Willis); Gull Island (^Smith^ ; whole 

 New England coast (^Slimpson). 



It is usuall}^ of a much smaller size than above mentioned. In- 

 deed, had it not been for a few large specimens sent me by Dr. L. 

 M. Yale, from Martha's Vineyard, which correspond in every re- 

 spect with specimens of L. rudis received from Mr. Sowerby, I 

 should not have recognized the species. The small specimens, such 

 as we usually find on the ocean rocks, answer well to Mr. Say's de- 

 scription of Turbo ob/ig-atiis, and were doubtless the shells intended 

 by him. They are usually darker colored, and more mottled, than 

 adult specimens. Mr. Say thought his specimens might be mere va- 

 rieties of his T. pal/iaius, with obtuse, elevated, revolving lines. He 

 must have inadvertently associated them with that species, to which 

 they have no affinity, instead of with his T. vesiitus, to which they 

 are closely allied, and from which they would not be distinguished 

 by the unpractised eye. The conviction that they are the L. rudis 

 has greatly diminished the number of what I had regarded as varie- 

 ties of L. tenebrosa. 



The variations consist in the greater or less prominence of the 

 revolving lines ; sometimes these are almost imperceptible, and at 

 others they would bear the name of ribs. The coloring is princi- 

 pally yellow, of various shades ; some small specimens are quite 

 white ; many are olive and gray. Dr. Loven has named a flesh- 

 colored variety L. incarnata. 



From L. paUiata it is distinguished by its more elevated spire, 

 and distinctly defined whorls, its striated surface, and the compres- 

 sion of the lip in front, so as to form an angle ; from L. tenebrosa, 

 20 



