300 LITTORINID^. 



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

 lialf the length of the shell ; the whole covered with regular, 

 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, somewliat 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. 

 " "'"'""' 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- 

 son} . 



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

 elongated form, its entire aperture, and the minute spiral lines with 

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

 der than, R. minuta. Brown figures two or three species 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 muUllineata, Stimpson, Bost. Proc. iv. 14 (1851) ; Check Lists, 4. 



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



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



Ijicularly ovate, peristome not thickened, effuse. Length, 



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



n inch. 



M This shell differs from R. acideus in being shorter ; its 



R^iuui "^^'lioi'ls ^^'6 much more compactly coiled, and its revolving 



imeata. striflB arc stronger and more evident. The lip is also more 



thickened. From R. Mighehii it differs in having much 



more numerous and crowded transverse striae. 



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

 near Nahant, on sandy and gravelly bottoms {Stimpson) ; Halifax 

 {Willis ). 



