LITTORINA. 37 



The shape is subglobose when young, and becomes more 

 or less obliquely globular-acute when adult. The shell 

 is never solid, but, at most, seems moderately strong : 

 the colouring is variable, the exterior being sometimes 

 clear yellow or orange, sometimes white, and sometimes 

 almost black ; it is occasionally, too, mottled with brown 

 and white (in which case the mouth is of a chocolate 

 colour). The more ordinary tints, however, range from 

 a somewhat olivaceous drab to intense brown, changing, 

 for the most part, into a darker hue upon the spire, and 

 a paler one at the base. Adult ringed or banded varieties 

 must be very rare, as we have never met with them, but 

 the younger shells are not unfrequently mottled, and 

 sometimes even streaked with white. The whorls, which 

 are five in number, are either encircled with numerous 

 raised wrinkles, which become almost obsolete on the basal 

 area, or else are girt with more or less strong and distant 

 ridges, that diminish in size below the basal declination. 

 The first three volutions are remarkably small, but the 

 penult becomes suddenly larger (being decidedly longer 

 than the nnited preceding ones), and, as well as the 

 body, much rounded. From this tumidity the suture 

 is peculiarly distinct, particularly in a variety, where the 

 body is horizontally flattened posteriorly. The apex is 

 very small, but is not prominently acute : the spire appears 

 to occupy, at most, a third of the entire dorsal length, 

 more frequently only a quarter, and a still smaller pro- 

 l)ortion in the younger examples. The base is not at 

 all produced, its surface is less convex than the portion 

 above it, and the commencement of its dechnation (usually 

 rather an abrupt one) is generally, in a slight degree, 

 subangulated. The aperture is rounded oval, not con- 

 tracted above, usually of a paler or darker chocolate- 



