6 
SHELL GALLERY. 
Economic 
Geological 
history. 
General 
distribu- 
tion. 
Helix desertorum. 
(See black table-case 1.) 
Desert-Snail from Egypt, was fixed to a tablet in March 1846, and 
in the same month of the year 1850 it was discovered to be alive. 
It must have come out of its shell in the interval, and finding it 
was unable to crawl away, had again retired within it, closing the 
aperture with a new epiphragm, but leaving traces of slime upon 
the tablet, which led to its immer- 
sion in water and subsequent re- 
vival, having passed a period of 
f our years in a dry museum with- 
out the smallest particle of food. 
The actual specimen is here figured, 
Fig. 1. 
The economic uses of molluscs 
to man are manifold, and will be 
mentioned in the course of the de- 
scription of the several families ; but here may be the place to 
direct the attention of visitors to side table-cases B and D at the 
side of the room, containing some specimens of articles manufactured 
from shells, such as cameos, flowers, bracelets, brooches, &c. 
Mollusca made their appearance on the globe at a very early 
epoch in the history of the development of animal life, a large 
number of fossil forms, such as Nautilus, Lituites, Orthoceras, &c, 
being found in the oldest Palaeozoic formations. Probably all these 
belonged to the Tetrabra?ichia, of which one descendant only, the 
Pearly Nautilus, has survived to our period. Some Gastropods 
and Bivalves coexisted with those ancient Tetrabranchs ; but these 
types abounded more in the later geological epochs, many Tertiary 
forms being un distinguishable from species which now exist. 
The greater number of Mollusca are inhabitants of the sea, 
some passing their whole life at the surface hundreds or thousands 
of miles away from land ; others at the bottom of the ocean at all 
depths, some having been dredged at five miles from the surface. 
much shallower water, and a large number 
Rivers and lakes furnish an immense variety 
numbers live on land in all situations — on 
forests, and deserts. 
Molluscs are either animal or vegetable-feeders, the former 
preying principally upon other members of their own class. 
Many are found in 
between tide-marks. 
of forms, and vast 
mountains, in valleys, 
* From 
& Son. 
Woodward's 'Manual of the Mollusca,' published by Lockwood 
