68 Lamarck's Genera of Shells. 



The olivse are very smooth shells, shining, and prettily coloured, 

 and have no epidermis. They are distinguished from the cylin- 

 drical cones, by the channel which separates the whorls of the 

 spire, and by the stria? on the columella ; from voluta and mitra, 

 by the spiral whorls of those shells being separated by simple un- 

 channelled sutures. The oliva is further distinguished by a pro- 

 minent callus at the upper extremity of the columellar lip, which 

 assists in forming the channel of the spire. At the base of the 

 columella some vestiges of the very oblique callus of the ancillarioe 

 appear, but those shells never have their sutures channelled, nor a 

 striated columella. 



The shell of the oliva is rolled round the longitudinal axis, leav- 

 ing a void space at the place of the axis, and the last whorl so en- 

 velopes the rest, that only their upper portion is visible, and con- 

 sequently the spire is very short. The shell appears to be formed 

 of two separate layers of testaceous matter, like that of the cyprsea, 

 for if we remove the exterior layer, we generally find the one be- 

 neath of a different colour. Hence, during the life of the animal, 

 the shell is probably frequently covered by the mantle, though no 

 dorsal line, indicating the junction cf'the lateral lobes of the mantle, 

 as on the cypra?a, can be distinguished on the oliva. 



Linneus not only did not distinguish the oliva? from his voluta?, 

 but even considered almost, all of them as mere varieties of one spe- 

 cies, viz., voluta oliva. This genus, however, is well defined by 

 the characters we have given above, though the discrimination be- 

 tween the several species is somewhat difficult. 



The oliva?, are found in the seas of warm climates ; the head of 

 the animal inhabitant is furnished with two long, pointed tentacula, 

 towards the middle of which, are placed its eyes. A tube, situated 

 above the head, conveys the water to the branchia?. 



Type. Oliva porphyria*. (Voluta porphyria. Linn.") 



Shell large, light flesh colour, spotted with red, and adorned 

 with red angular lines ; spire and base tinged with violet. South 

 American Seas. PI. v. Fig. 207. 62 Recent species, and 5 fossil. 



* Of porphyry. 



