68 NATURAL HISTORY. [UPPER FLOOR. 
construction, which consists of a number of cells piled one 
on the other; and in having no terminal cavity for the 
reception of the body of the animal. 
The remainder of the Table is occupied by the shells of 
those Mollusca which live on animal food, and have their 
branchiae placed on the internal part of the mantle, over 
the front of the back of the neck. 
These shells are always provided with a canal in front of 
the mouth, which covers the syphon of the mantle, as in 
the Pelican's foot ( Aporrhais ) and the various species of 
Murices and Buccina. The larger species are used as food 
by the natives of the sea-coast, and by the fishermen as 
bait. In Scotland the shell of the large Fusus despectus 
is used as a lamp. The animal of Purpura Lapillus yields 
a beautiful purple colour, which has been considered as the 
Tyrian dye of the ancients ; but there is little doubt that 
this colour was obtained from various species. The eggs 
of these animals are contained in coriaceous cases, and the 
cases of the Buccinum undatum , and Fusus despectus have 
been mistaken for the eggs of the oyster, and called oyster- 
spat* This error is the more remarkable, as oysters are 
viviparous, the young being found in the branchiae of the 
parent in the month of July : the egg of Purpura Lapillus 
has, by a similar error, been described as a species of Tu- 
bularia. All these egg-cases are in the collection ; they 
contain many eggs, of which only a few gradually 
enlarge and come to perfection. 
The larger species of the preceding shells are extremely 
apt to vary according to the roughness or smoothness of the 
sea they live in; thus, some of the common Whelks are 
thick and rugose, others very thin, even, and finely 
coloured. Rarely the whorls of these shells turn contrary 
to the common direction, from left to right, and sometimes 
when the shell has been injured in its growth, the succeed¬ 
ing whorls are turned out of their usual course, and the 
shell becomes very much elongated. Most of the speci¬ 
mens of Fusus despectus are smooth, but some are spirally 
keeled; the smaller species vary in a similar manner, but 
the differences are not so striking. The cowries [Cyprcea), 
and the Tear-Shell ( Erato ), are remarkable for the young 
shells being very thin and exposed, whereas the adults are 
covered with a thick coat, deposited over their back by the 
