SHELL GALLERY. 57 
The collection is contained in four parallel rows of table- 
cases, the arrangement commencing on the right as the gallery 
is entered. The first two rows contain the marine forms of 
Gastropods — a division which includes Snails, Slugs, Whelks 
(iig. 28), and all those Molluscs which crawl upon the under 
surface of their bodies ; the Cones, Volutes, Mitras, and Murexes 
forming some of the most attractive groups. The two rows of cases 
on the left contain the Land-Shells, Bivalves, and Cephalopods. 
The Cockles, Oysters, Clams, Piddocks, Teredos, Scallops, and 
Ark-Shells represent some of the principal types of Bivalves, 
so called on account of their shells being formed of two pieces 
or valves. A Giant Clam (fig. 29), on the floor of the gallery. 
Fig. 30. — The Peaely Nautilus (Nautilus pomp ilius). 
a, body ; h, siphuncle ; c, eye ; d, hood ; e, tentacles ; /, muscle of attachment 
to the shell ; g, siphon. 
weighs 310 lbs. The Argonaut, the beautiful Pearly Nautilus 
(fig. 30), the Octopus, Squids, and Cuttlefishes are the chief kinds 
of modern Cephalopods ; but there are a number of fossil forms, 
most of which are exhibited in the Geological Department. 
In the same gallery are exhibited three other groups of marine Sea-Mats, 
organisms, respectively known as Polyzoa, Brachiopoda, and and^seS^^ 
Tunicata. Many of the former live in colonies, and are squirts, 
known as Sea-Mats. They are often mistaken for sea- weeds, 
although they are really animals of high organisation. The 
Brachiopods have two shells like bivalve Molluscs, only the 
valves are dorsal and ventral — that is to say, back and front 
— instead of right and left. One valve is frequently per- 
forated, hence the name of " Lamp-shells." Sea-squirts, 
