UNIVALVE MOLLUSCA. 455 
The shells of the less marked species are frequently used in India as 
lime for making mortar, under the name of Chunam. 
Our space only permits us to mention, among the more curious 
species, Cassis canaliculata (Fig. 281), two varieties of Cassis Mada- 
gascariensis (Figs. 282 and 283), and the curious Cassis Zebra 
(Lam.), or Zebra-marked Casque (Fig. 284). 
The Purpuras have a classical name and history, having furnished 
the Greeks and Romans with the brilliant purple colouring matter 
which was reserved for the mantles of patricians and princes. The 
genus Purpura is characterised as possessing an oval shell, thick 
pointed, with short conical spiral, as in Purpura lapillus (Fig. 285). 
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, ter- 
minating at its lower extremity in an oblique notch. The columellar 
edge is smooth, often terminating in a point; the night 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 
middle of their external side. Its toot is large, bilobate in front, 
with a semicircular horny operculum. 
The species of Purpura inhabit the clefts of rocks in marine 
regions covered with alge. On occasions they bury themselves in 
the sand. They creep about by the help of their foot in pursuit of 
bivalves. They are found in all seas; but the larger species and 
greatest numbers come from warm.regions, more especially from the 
West Indian and Australian seas. 
The Purpura of the ancients was not, as is generally thought, a 
vermilion red, but rather a very deep violet, which at a later period 
came to have various shades of red. The secret of its preparation 
was only known to the Phcenicians, that being most esteemed which 
came from Tyre. Sir William Wilde has discovered on the eastern 
shores of the Mediterranean, near the ruins of Tyre, a certain number 
of circular excavations in the solid rock. In these excavations he 
found a great number of broken shells of Afurex trunculus. He 
thinks it probable that they had been bruised in great masses by 
the Tyrian workmen, for the manufacture of the purple dye. Many 
shells of the same species are found actually living on the same coast 
at the present time. 
Aristotle, in his writings, dwells upon their purple dye. He says 
that this dye is taken from two flesh-eating molluscs inhabiting the 
sea which washes the Phcenician coast. According to the description 
given by the celebrated Greek philosopher, one of these animals had 
