I 79 1 
itself up like a wDod-louse, The margin between the shell and 
the edge of the foot is ^^tudded with close-set spines. The name 
* Amphineura ' refers to the two pairs of nerve trunks which run 
along the length of the btniy of these animals. The Museum 
possesses specimens of Chiton spiniger from Sumatra and the 
Lankawi Islands, presented by Mr. E. Rostados in 1 897, and 
from South Pagi, presented by Mr, Kloss in 1 902. They are 
about 3 inches in length, 
SNAILS (Gastropoda.) 
The snails are by tar the largest class of the Molluscs. 
Their body is asymmetrical and is covered by a shell which 
consists of a single piece and is usually spirally coiled. In 
some cases the shell may be very small or may have disappear- 
ed altogether, as in the Slugs. The name * Gastropoda ' refers 
to the well-developed muscular foot upon which the animal 
rests and by the continual contraction and expansion of which 
it moves along. Thousands of species live on land and in fresh- 
water, but the great majority (about 757') are marine. 
The marine forms breathe by means of gills, the terres- 
trial ones have lungs, whilst some freshwater species (P<j/wifi>w) 
have gills and others lungs {Limnaea, Plamrbis), showing thus 
a derivation from marine and terrestrial ancestors respectively. 
One freshwater species even possesses both gills and lungs ; 
this is the large and almost spherical snail which is so common 
here in rivers and swampy places {Ampullaria), The so-called 
* lungs ' of the Gastropods are, however, quite different from 
those found in Vertebrates, and are not spongy organs. They 
consist of a sack the roof of which is formed by the mantle and 
is overspread by a network of blood vessels. The cavity of the 
sack is called the ' pulmonary cavity *. It opens to the outside 
by the ' respiratory aperture,* 
Many snails possess an ' operculum,' i.e, a horny or 
calcareous disk attached to the foot by means of which the 
opening of the shell can be closed when the animal has with- 
drawn itself. Some opercula are of considerable thickness and 
are manufactured into buttons and simple ornaments. 
According to their respiratory organs the Gastropods are 
subdivided into four orders : 
(1) The Scutibranckiatii are thus named from the gills 
being arranged in a circle between mantle and foot, this being 
the case at least in the most typical member ol the order, the 
Limpet {Patella). The Limpets are some of the most charac- 
