144 IXTRODrCTION TO COXCHOLOGY. 



Naturalists who visit the wild shores of Greeulaud and 

 Spitzbergen may find the Margarita, one of the most con- 

 spicuous among their molluscous fauna^ in many a wild sea- 

 cove shaded with rocks, that yield the cochlearia and sorrel, 

 those invaluable plants, which uniformly grow together. 

 The species which thus braves the extremity of northern 

 winters, belongs to the first group into which the various 

 species that pertain to the genus Margarita are divided, and 

 may readily be recognized by a rather light and spiral 

 structure, largely umbilicated, and resembling the form of 

 Cj/cJostonia. 



The second group is distinguished by a more sohd 

 growth, having a porcellaneous surface, with the umbilicus 

 filled up by a callous deposit. Unlike the first, which 

 affect a northern latitude, the species inhabits a warm region, 

 its colours ai-e more vivid, and many of the indidduals are 

 elegantly striped: the M. tceniata, for example, is enchcled 

 by fillets of bright red, and the M. jjulcliella, by alternate 

 bands and lines of dark violet -blue. 



The animal inhabitants of Turho, Trochus, Belj-jhrnula 

 Margarita, and Monodonta, are so nearly similar, that 

 questions have arisen with regard to the propriety of sepa- 

 rating them. The head of each has a blunt proboscis-like 



