LITTORINA. 35 



forms, is coarsely aud sharply ridged, has a rather more 

 abbreviated or globose contour, and a rather larger aper- 

 ture. The colour is usually of an uniform scarlet or 

 brown, but sometimes the ridges are white, whilst their 

 intervals (as well as the mouth of the shell) are of a 

 chocolate or dark brown tint. The basal declination is 

 abrupt and subretuse. There are only four or five volu- 

 tions, which are very distinctly defined ; those of the spire 

 are very short, so that the body is usually twice the 

 length of the rest united, a character that distinguishes the 

 shell from the ridged variety of tenebrosa, wherein the 

 smaller whorls are much more produced. The princii^al 

 ridges (those above the basal slope) are about six in 

 number, and are separated by rather broader interstices. 

 The mouth is rounded oval, and very projecting ; the 

 pillar is broad ; the base a little produced. 



The animal difl:ers from that of the preceding species, in 

 being of a lighter hue, with the exception of the head, 

 which is more uniformly dusky. The dark markings are 

 not arranged in bars, and the tentacles instead of being 

 ringed, are dusky, with a pale yellowish line down the 

 centre of each. The edge of the muzzle and base of the 

 foot are yellowish, or yellowish white. Mr. Clark has 

 observed that this animal, unlike the last, is viviparous ; 

 " in July and August all the ovaria are full of completely 

 formed young shells." 



The Littorina rudis is found almost everywhere on 

 stony and rocky shores, often in considerable numbers, 

 though not strictly gregarious. It inhabits the first and 

 second subregions of the Littoral zone, those of Fucus 

 canaliculatus and Lichina, usually below the next species, 

 and always within the reach of the tide. Its continental 

 range is like that of littorea. 



