352 LITTORINID^. 



and depressed, sunk within the upper margin, the base of the 

 shell or lower part of the mouth being placed in front of the 

 observer : whorls 3-4, convex, the last disproportionately large 

 and occupying nearly the whole of the spire : suture well de- 

 fined : mouth exceedingly large and capacious, equal in size to 

 the closed part of the shell ; the base is somewhat angular, 

 especially in immature specimens : outer Up thin, incurved 

 towards the pillar : inner Up thickened or callous above the 

 canal, over the upper part of which it is folded, not united 

 with the outer lip : pillar white ; canal very wide and extend- 

 ing funnel-wise into the interior of the spire, so as to expose 

 the greater part of it : inside polished, and coloured like the 

 outside : operculum having from three to four whorls, wrinkled 

 across, and indistinctly marked with very minute and close- 

 set spiral lines. L. 0*45. B. 0-35. 



Var. 1. neritoidea. Grass-green, much smaller, and less 

 expanded, resembling in shape Neritina fiuviatilis, and having 

 a rather prominent but short and eccentric spire. L. neritoidea , 

 Gould, Inv. Mass. p. 263, f. 170. 



Var. 2. patula. Olive-green, rather more solid, with a flat 

 spire and the expansion outwards being not so much in front 

 as above and below, making the outline that of an equal-sided 

 triangle ; canal nearly closed in the adult. " Variety ? Pa- 

 tula" Thorpe, Brit. Mar. Conch, p. 37, f. 83. 



Var. 3. albescens. Of a paler hue or white, smaller but 

 shaped like the last variety. 



Habitat : On Laminarice and other sea-weeds having 

 flat and smooth fronds, at low-water mark and in a few 

 fathoms seawards, chiefly on our southern and western 

 coasts, but also in St. George's Channel, all round Ire- 

 land, the Clyde district, and Frith of Forth ; Kent (Da 

 Costa and Boys) ; Northumberland and Durham (Al- 

 der); Aberdeenshire (Macgillivray); Orkneys (Forbes). 

 Var. 1. West of Scotland and Shetland. Var. 2. Tor- 

 quay and Sunderland (Hanley); Guernsey, Langland 

 bay near Swansea, and Barmouth (J. G. J.); Bantry 

 bay (Barlee). This variety seems to connect the present 

 species with Littor'ma obtusata. Var. 3. Skye and the 



