LITTORINA. 83 



This strong shell closely resembles the preceding, but 

 does not attain to its size, and chiefly differs from it in the 

 roundness of its well-defined volutions. It is sometimes 

 almost smooth, sometimes spirally girt with indistinct cos- 

 tellar strife (in which case those upon the base are the 

 most prominent) and very rarely (yet occasionally in an 

 orange and livid banded variety, where the ridges are 

 obsoletely subtubercular) strongly costellated. The colour 

 ranges from yellowish-white to orange, and is either uni- 

 form or banded with about two or three zones of liver- 

 colour or chocolate, of which one at least is broad ; the 

 throat varies in tint from chestnut to dark chocolate- 

 brown ; the peristome in the paler varieties is pure white, 

 in the darker ones is tinged with different intensities and 

 shades of liver-colour. Occasionally also (but not com- 

 monly) the shell is livid and the zones, if present, pale 

 yellow. 



The form of the most typical examples is subglobose- 

 conic, but, as in the common periwinkle, the spire varies 

 greatly in relative height, and the more produced it is, 

 the longer is the shape of the body. The basal portion 

 of the body is almost always flattened, narrowed, and 

 rather elongated ; when the cessation of roundness is 

 abrupt, a slight angularity is perceptible upon the final 

 whorl. The mouth of the adult is small in proportion 

 to the extent of its outer circumference, the cavity being 

 greatly diminished through the space occupied by the 

 thickened basal junction of the two lips ; it is rounded 

 oval (more rarely circular) and not contracted posteriorly. 

 The junction of the outer lip, which is acute, disposed 

 to expand, and more arched posteriorly than anteriorly, 

 is subrectangular ; hence its ordinary marked projection. 

 The attached edge of the columella is often a little ele- 



VOT,. Til. F 



