384 



BUCCINOID^E. CASSIS ; PURPURA. 



FIG. 581. CASSIS TUBEROSA. 



found on the coast of the Mediterranean. They live at some 



distance from the 

 shore, on the sand, 

 into which they 

 occasionally bur- 

 row, so as to hide 

 themselves. The 

 shells of the Cassis 

 rufa and other 

 species are beauti- 

 fully sculptured 

 by Italian artists, 

 in imitation of 

 antique cameos ; the different layers of colouring matter which 

 they contain, strongly resembling in hue those of the onyx and 

 other precious stones formerly used for this purpose. Of these, 

 a great variety of ornaments are made ; and of late years a con- 

 siderable trade has been carried on in them on the Continent. 

 Numerous other genera may be associated in the same group ; 

 but it will be sufficient here to notice the Purpura, a shell of 

 comparatively small size, but which is very abundant in some 

 situations on our own coast and elsewhere. The total number 

 of known species exceeds fifty ; the largest among them are 

 inhabitants of tropical seas. It was from the animals of this 

 genus that the Roman purple dye was obtained ; and a small 

 quantity of this may be found in the Purpura lapillus of the 

 British coasts. All the Mollusks of this group, so far as is at 

 present known, have the habit of depositing their eggs in egg- 

 cases, or nidamenta; which are of various forms in the different 

 species, and are attached in different modes. That of the 

 Buccinum is often to be met with on our shores, in the form of 

 a large irregular ball, composed of a number of little vesicles 

 attached together, each containing several eggs. The Purpura 

 forms a large number of distinct cylindrical cases, which it 

 attaches to the rocks it infests. 



925. The last group comprised in this extensive family is 



