550 ianthinid,e. 



he has, however, changed the name of his type to /. com- 

 munis, and mingled the synonymy of the present species 

 with that of the West Indian shell (characteristically 

 enough represented by Chemnitz, vol. v. f. 1577, 1578), 

 which, from our studj^ of the Linnsean cabinet, we know 

 to be the original ianthina of the Swedish systematist. 

 We would suggest, then, the advisability of retaining the 

 appellation of fragilis for that shell, and continuing that 

 of communis to this far more abundant Mollusk. 



Although thin and fragile, this shell is comparatively 

 strong for its genus. The dark violet or purple hue of its 

 basal superficies is exchanged upon its upper surface for a 

 much paler tint ; but whilst the superior or narrower 

 portion of each whorl is almost white, the lower part is 

 more or less stained with the characteristic generic colour- 

 ing : in our smaller British examples a rather broad band of 

 white encircles the axis. The shape is orbicular-conoid, and 

 is horizontally compressed and generally but little rounded 

 at the base. The surface is moderately glossed. Rather 

 remote spiral lines, that are chiefly conspicuous upon the 

 lower surface, and frequent irregular stria? that follow the 

 lines of growth, are more or less apparent upon the ex- 

 terior ; besides these are some most minute and densely 

 disposed spiral striula? in the interstices of the stronger 

 ones, but these are generally obsolete in the adult exam- 

 ples. There are from four to four and a half volutions, 

 that rapidly enlarge from a very small, obtuse, and 

 distorted apex. The chief breadth of each whorl is at its 

 bottom, and not towards the middle, as there is an almost 

 continuous plano-convex shelve from suture to suture ; 

 some few of our smaller examples, however, exhibit a 

 slight shoulder, but we are inclined to regard this as 

 exceptional. The proportion between the spire and the 



