94 UNIVALVES. 



ment of these ornaments. In one division, the 

 shells are distinguished by having two varices in 

 each whorl, continued in a longitudinal series on 

 each side up to the apex, giving them a flattened 

 appearance on the front and hack ; the genus 

 which they now constitute is called Ranella * 

 Frog, from the resemblance of the shells to that 

 animal. 



The shells of another division f are distin- 

 guished by three rows of varices, which sometimes 

 expand into elegant foliations sometimes into 

 lengthened spines ; the varices of this family of 

 shells are so arranged that they form three lon- 

 gitudinal raised lines taking rather an oblique in- 

 clination towards the apex. It is evident that 

 the habits of the mollusca of these two sets of 

 shells must be different, for the situation of the 

 varices of the latter proves that a smaller portion 

 is added to the abode at each epoch of its growth 

 than in the Ranella. 



A third division J of this genus includes shells 

 ornamented by varices, not disposed in a con- 

 tinued series from the apex to the base as in the 

 other two classes. This difference in the dispo- 

 sition of these protuberances is occasioned by the 

 piece which the animal adds to its shell being 

 more than half a volution. The varices are con- 

 sequently few, and appear scattered over the shell. 



* Plate IV. fig. 2. f Plate IV. fig. 1. 



J Plate IV. fig. 3. 



