PURPURA. 



and often internally rather sharp-edged. Operculum horny, 

 with a lateral nucleus, thinnest on the edge nearest to the 

 columella. A very variable, and in some species very 

 strong and thick horny epidermis covers the outside. 



The following are the characteristics of the six 

 divisions of this Genus mentioned by Duclos^ first, those 

 which are transversely grooved, such as P, succincta. Lam. 

 (Buccinum Orbita, nonnull,) secondly, those which are 

 longitudinally ribbed, as P. Nassatula; thirdly, the 

 scalariform, in which the volutions resemble a winding 

 staircase ; fourthly, those with numerous spinose tubercles 

 on the outer surface, such as P, Hippocastanum, (which 

 leads to Ricinula); fifthly, such as are granose outside, of 

 which P. Morus [Ricinula Morus, Lam ) is an example ; 

 and lastly the Bucciniform of which Duclos cites the P. 

 cataracta as characteristic. 



Purpura appears to us to be related to Miirex, Bucci- 

 num and Trichotropis J but it may be distinguished by its 

 operculum in most cases, and by the peculiarities of its 

 columella in others. We have already pointed out its 

 distinguishing charac^ters. To Monoceros also it bears 

 considerable resemblance^ indeed there are some species 

 which have the peculiar horn which characterizes Mono - 

 ceros according to Lamarck, and in other respects entirely 

 resemble Purpura : we are rather disposed to think that 

 the horn ought not to be regarded as a generic character, 

 for we know that it is very variable; indeed we find a 

 similar horn in some species of Murex, as well as in some 

 Turbinelli, and there is a very handsome Purpura, which 

 has been called Monoceros grandis which has a very 

 distinct horn, but in all other respects is a true Purpura. 



Fossil Purpura are very scarce, and as far as we know 

 they all belong to the tertiary beds. 



