430 THE OCEAN WOKLD. 



The head of the animal is large and thick, furnished with two 

 conical elongated tentacles, at the base of which are the eyes. The 

 mantle is ranged outside the shell, falling 

 back upon the edges of the opening, and 

 terminating at its anterior extremity in a 

 long cylindrical channel, cloven in front, 

 and passing by a hollow at the base into the 

 bronchial cavity. The foot is large, and 

 furnished with a horny operculum. 



These animals keep near the shore, in 

 shallow water. They walk slowly, and often 

 sink themselves into the sand, where they 

 prey upon small bivalves. They are not 

 numerous in species; but specimens from 

 the Indian Ocean are often large and beau- 

 tifully marked. The shells of the less marked 



species are frequently used in India as lime, and employed as mortar, 

 under the name of Chunam. 



Our space only permits us to mention, among the more curious, 

 Cassis canaliculata (Fig. 273), two varieties of Cassis Madagas- 

 cariensis (Figs. 274 and 275), and the curious Cassis undaia 

 (Martini), Zebra (Lam.), or Zebra-marked Casque (Fig. 276). 



PUBPUBA. 



The Purpuras have a classical name and history, having furnished 

 the Greeks and Eomans with the brilliant purple colouring matter 

 which was reserved for the mantles of patricians and princes. The 

 Purpura is an oval shell, thick pointed, with short conical spiral, as in 

 Purpura lapillus (Fig. 277). In some it is tubercular or angular, the 

 last turn of the spiral being larger than all the others put together. 

 The opening is dilated, terminating at its lower extremity in an 

 oblique notch. The columellar edge is smooth, often terminating in 

 a point ; the right edge often digitate, thick internally, and folded or 

 rippled. 



The animal presents a large head, furnished with two swollen 

 conical tentacles, close together, and bearing an eye towards the 



