54 



Family 3. PURPURIFERA. 



Shell ; terminating at the base, either with a short slightly ascend- 

 ing canal, or loith a deep sinus. 



The genera enumerated under the head of Furpurifera, are grouped 

 together upon a very artificial basis; the animal is characterized by a 

 variation of form wliich it is difficult to reconcile with the propriety of 

 their being associated in the same natural family, and the sheU is scarcely 

 less dissimilar in its general aspect. In Terehra the shell is of a smooth 

 elongated lanceolate growth, whilst in Harpa it is of an ovate ventricose 

 structure, thickly studded with varices ; the only distinguishing character 

 of the family, therefore, as constituted by Lamarck, resides in the basal 

 sinus, that posterior portion of the slieU wliich is fitted to the passage of 

 the respiratory siphon, conveying water to the braucliial cavity. 



The soft parts of the Purpurifera, as in most of the molluscous tribe, 

 display a striking contrast of colouring compared with the shell, and the 

 relation of form is equally remote; in Bollum, the animal is green or 

 mottled-blue, colours of which there is not the sHghtest approximating 

 tinge in the sheU ; it is also characterized by an ample muscular disc, and 

 a remarkable elongation of the proboscis, terminating in the B.perdix with 

 a flattened fimnel-Hke rosette, wliilst the sheU is chiefly distinguished for 

 its comparative tenuity. The animal of Harpa has a beautifully coloured 

 ocellated disc, extending in a remarkable degree beyond the posterior ex- 

 tremity of the shell to nearly a peak. In some of the Buccina the disc is 

 expanded on either side of the aperture, and truncated behind forming 

 a flat square ; in Oliva and Ancillaria we have a modification of the ventral 

 disc somewhat analogous to the lobate structure of the Cowrey, which being 

 reflected into an ample fold, though generally partially retracted, is suffi- 

 ciently capacious to envelope the shell ; in Magilus, on the other hand, 

 the locomotive and calcifying organs are extremely Hmited in their dimen- 

 sions, owing to the confined nature of its habitation, although the latter is 

 exercised with a degree of energy which is truly wonderful. 



The genera at present referred to this family are as follows : — 



