110 LITTORINID.'E. 



are closely set, and for the most j)art are broader than 

 their narrow and perfectly smooth intervals. In general 

 they are wont to become obsolete on the upper part of the 

 antepenult, and more especially upon and towards the 

 slowly contracted and somewhat produced base of the 

 body- whorl. The spire, which is attenuated to rather a 

 fine point, that is sometimes white, sometimes purple, 

 is composed of six volutions, that barely equal the length 

 of the body- whorl, are but little convex, except that the 

 penult turn swells out a little towards the lower suture, 

 and are well defined by a simple separating line, that 

 becomes rather broader and stronger as it descends. The 

 mouth, which occupies about one-half of the entire length 

 of the shell, is large and subovate ; its throat is smooth, 

 and of a pure porcelain-white. The outer lip is margin- 

 ated behind, but is thin at the edge, which is disposed to 

 expand, especially at the rounded and projecting anterior 

 extremity. The pillar-lip is much reflected, but with no 

 distinct umbilical chink behind it ; it is rather long, broad, 

 shelves much inwards, and is furnished with a more or less 

 distinct fold, that lies rather below the middle of the aper- 

 ture. We possess a stunted form of this variety, in which 

 the spire occupies only two-fifths of the shell, and the big 

 mouth is edged internally with dirty purple. 



The thinner or membranaceous variety affects muddy 

 estuaries. It is usually more or less devoid of ribs, is 

 pale fulvous, and often variegated with obliquely flexuous 

 rufous lines, which in intermediate examples meander 

 between the almost obsolete costse. The fold of the 

 pillar-lip, which has occasionally a ruddy hue, is usually 

 less developed than in the more solid individuals. Both 

 in this and the typical form the longitudinal increase of 

 the whorls, which nowhere exhibit the slightest trace of 



