34 LITTORINID.?.. 



vatcd, ami is coinparatively straight (in liitorea it is mucli 

 arcuated). Tlie pillar is plano-concave, and abruptly 

 dilated, being remarkably broad at the anterior base, 

 where it is often disposed to become slightly effuse and 

 to twist a little to the left. The parietal enamel is gene- 

 rally rather thick in adult individuals. The throat is 

 quite smooth. An umbilicoid indentation is occasionally 

 perceptible. 



Our largest specimen only measures nine lines and a 

 half in length, and eight lines and a third in breadth. 



We are inclined to regard the mgrolineata, as defined 

 by Philippi, as an aberrant form of this species. The 

 chief peculiarity arises from the spiral sculpture being 

 elevated into regular ribs that are separated by profound 

 sulci, and are often bifid near the outer lip. At times, 

 too, the angle formed by the junction of the outer lip with 

 the body is almost as acute as in littorea, from which 

 the shape of the pillar and the anterior filling up of the 

 aperture suffices to distinguish it. The most characteristic 

 style of colouring is where the shell is tawny, and the sulci 

 brown or almost black ; sometimes, too, the entire shell 

 is pure white, or painted with two broad fulvous zones ; 

 sometimes of a bright yellow, either with or without two 

 broad spiral bands, in whose livid tint the projecting costa) 

 do not, for the most part, participate ; the margin of the 

 mouth in the banded examples is more or less stained with 

 reddish purple. 



The shell figured nsjur/osa, in Montagu's " Supplement 

 ([)1. 20, fig. 2) to the Testacea Britannica " (not that ori- 

 ginally described as such), looks like an aberrant ridged 

 variety of this very variable species. At least what we 

 suppose to be identical (pi. LXXXVI. fig. 1) appears to be 

 so. It is smaller and rather less solid than the more typical 



