LITTORINA. 145 



marked with black waved lines ; the Diuzzle is rather short, 

 broad, and straight in front; the pyramidal tentacles are 

 ringed with the black lines ; they are blunt-pointed at the 

 apex, but thick at the base, where they have a very thick 

 swelling, on which the bright little specks of eyes are placed. 

 Throwing back the pointed hinder part of the whitish foot, 

 which carries away the horny door with it, the periwinkle 

 lifts his heavy shell over his back, and crawling away is soon 

 out of sight. 



One remarkable circumstance connected with the history 

 of this and several other species is, the great variation of form 

 which it is apt to assume in some positions ; for although 

 going to a fishmonger and purchasing a pint of periwinkles 

 from his stock, we do not often find any great deviation from 

 the common well-known type, yet, in some cases, where 

 disturbing inflnences have introduced an undue influx of 

 fresh water, the most varied forms occur. 



The wildest cases of eccentric formation, however, met 

 with on our modern shores, are symmetry itself compared 

 to those of more ancient seas. Among the periwinkles of 

 the crag are some specimens so different from each other, 

 that it would seem impossible to recognize them as belonging 

 to the same genus. Some are quite pyramidal, others have 



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