52 
Tanks No. 3, 22 and 24. 
the sole of a foot and is used for crawling, which is generally the only 
means of locomotion possessed by the Snails. In many forms the viscera are 
contained in a spirally coiled, calcareous shell, the snail-shell, into which 
the rest of the body can be retracted. The shell is secreted by the mantle, 
a flap of the skm, and is held on the 
The foot frequently carries a horny 
mouth of the shell when the body of 
Fig. 82. Haliotis tuberculata, 
V 2 nat. size. Tank 22. 
animal by means of a spiral muscle, 
or calcareous lid, which closes the 
the animal is retracted. The col- 
Fig. 83. Cassis sulcosa, Y 2 nat. size. 
Tank 3. 
lections of shells in museums give some idea of their beauty and bril¬ 
liant colouring, as also of the great variety of their forms; most 
are marine. The most important ones found in the Aquarium are the 
following. 
The Ear-shell, Haliotis (Fig. 82, Tank 22), has a very flat ear-shaped 
shell with a large opening, and a row of holes through which tentacle¬ 
like processes of the foot protrude. Internally the shell is coated with 
Fig. 84. Natica millepunctata, Fig. 85. Murex brandat'is, 
Y 2 nat. size. Tank 24. 4 /2 nat. size. Tank 3. 
the most lovely mother-of-pearl, and is therefore frequently used for orna¬ 
mental purposes. 
The Helmet-shell, Cassis (Fig. 83, Tank 3), is also commercially a 
very important shell. The shells of the largest specimens are used in 
the cutting of the well known' cameos. Suitable pieces are sawn out of 
the shell and their outer surface ground down, while the inner surface 
remains in its natural condition; the relief is worked out of the many- 
coloured layers by means of a graving-tool such as is used for cutting corals. 
The Snail Natica (Fig. 84, Tank 24) possesses in so high a degree 
the power to take up water into the cavities of its foot, that it becomes 
