54 
SHELL GALLERY. 
is entered. The first two rows contain the marine forms of 
Gastropods — a division which includes Snails, Slugs, Whelks 
(fig. 28), and all those Molluscs which crawl upon the under 
surface of their bodies ; the Cones, Volutes, Mitras, and Murices 
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, 
weighs 310 lbs. The Argonaut, the beautiful pearly Nautilus 
(fig. 30), the Octopus, Squids, and Cuttlefishes are the chief kinds 
Fig. 30. — Pearly Nautilus (Nautilus pompiliui). 
a, body; h, siphuncle ; c, eye ; d, hood; e, tentacles; /, muscle of attachment 
to the shell ; g, siphon. 
of modern Cephalopods ; although there are a number of fossil 
forms, most of which are exhibited in the Geological Department. 
Marine In the same gallery are exhibited three other groups of marine 
Organisms. organisms, respectively known as the Polyzoa, Brachiopoda, and 
Tunicata. Many of the former live in colonies, and are commonly 
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 perforated, hence the name of "lamp-shells." 
Tunicates, or Ascidians, are worthy of the best attention of the 
visitor, on account of their evident affinity with the vertebrate 
