300 LITTORINID^. 



the two upper forming a blunt apex, the lowest rather more than 

 half the lenoth of the shell ; the whole covered with reaular, 

 crowded, microscopic revolving lines ; aperture one third the length 

 of the shell, oval, oblique, angular behind, the margin simple and 

 entire, barely touching the preceding whorl, somewhat ex- 

 panded, and on the left side elevated, and slightly turned 

 over an umbilical depression or chink ; operculum horny. 

 Length, three twentieths of an inch ; breadth, one fifteenth 

 of an inch ; divergence, twenty-three degrees. 



R. aculeus. i • f i • 



Found sparingly on the partially decayed timbers of an 

 old wharf; and plentifully on stones, about low-water mark, at East 

 Boston. Gull Island {Smith'); whole New England coast {Stimp- 

 soti) . 



It is a small, but well-characterized shell, distinguished by its 

 elongated form, its entire aperture, and the minute s|)iral lines with 

 which it is covered. It is nearly as long as, and much more slen- 

 der than, R. Diinuta. Brown figures two or three sj^ecies which 

 closely resemble this. 



[Animal white throughout, head moderately produced, deeply 

 bifid ; foot very little dilated at anterior angles ; eyes black ; mo- 

 tions very moderate ; swims inverted at surface. 



Rissoa multilineata. 



Rissoa multilineata, Stimpson, Bost. Proc. iv. 14 (1851) ; Check Lists, 4. 



Shell minute, oblong-ovate, blunt, white ; whorls five, convex, 

 marked with about twenty minute, transverse strioe ; aperture or- 

 bicularly ovate, peristome not thickened, effuse. Length, 

 ^'^ ^^ ■ one tenth of an inch ; breadth, forty-five thousandths of an 

 inch. 



This shell differs from R. acnleus in being shorter ; its 

 . whorls are much more compactly coiled, and its revolving 

 imeata. sti'ise ai'C strougcr and more evident. The lip is also more 



Enlarged. ^ '- 



thickened. From R. Mig-helsii it differs in having much 

 more numerous and crowded transverse stria?. 



It was dredged in five fathoms, off Great Misery Island, and also 

 near Nahant, on sandy and gravelly bottoms (^Stimpsoti) ; Halifax 

 {Willis). 



