[ 82 ] 
much variation in their markings, from the Great Natuna I., 
presented by Mr. V. Knight in IQO;, is exhibited To the other 
Ti'ctibrdnchiata belongs the Sea-Hare {Aplysia) in which the shell 
is represented merely by a thin plate covering the gills. The 
papular name is due to a fancied resemblance of the Mollusc 
to a crouching hare. A very large specimenj from Marudu 
Bay, B, N. Borneo, presented by the late Mr. R. M. Little in 
[895, is exhibited. It measures now/, in spirit, 5H inches in 
length, though, when alive, it Vifas probably quite half as big 
again. The Nudtbrimchiata are all without sheJl, and both in 
this respect and in their externa! symmetry they resemble the 
Land Slugs to which we shall come presently. But whilst the 
Land Slugs are not remiirkable for their attractiveness, no 
more beautiful objects can be imagined than a Nudibranch in 
its natural element. Not only is their colouring beyond des- 
cription, but so is also the graceful form of their body» with the 
variously shaped tentacles, gills and other dorsal appendages 
fully expanded. Unfortunately little of the colour and shape 
of these animals remain when they are preserved in spirit. 
The species belonging to the genera Dori% Kaiirodoris^ Casetla, 
l^hikohnmchiL^ and Elysia are amongst the more common ones 
which may be collected at tow tide in the close neighbour h(x>[i 
of Singapore. 
(4) The PulnioHdta breathe by means of lungs. Most 
of them are terrestriaU some live in freshwater and very 
few are marine. They never have an operculum and can thus 
readily be distinguisiied from the other Gustropoda which live 
on landt like Cydopiwrus (see p. 80), or in freshwater, like 
Ptdudiiui (see p. 80), Many of them have a resting stage, 
in cold climates during the winter {hibernation), in hot 
climates during the summer (aestivation). The shell-bearing 
forms withdraw into their shell during this resting period and 
close the mouth of the shell with a lid. the so-called epiphragma. 
This lid, however, has nothing to do with the operculum. It is 
formed by a slimy secretion, containing lime. — The freshwater 
species breathe in the same way as the land Ptdmonata and 
have to rise to the surface to do so. They can be drowned if 
prevented in this, though there are some exceptions to this rule- 
More than 7000 Pulmonates are known. They are found 
all over the globe, though they prefer localities with abundant 
lime and moisture. Specially rich in them are certain groups 
.of islands, like the West Indian Islands, the Philippines and 
the Sandwich Islands. More than one half of them belong to 
the well-known genus Helix, 25 species of Hdi'X occur In 
