GASTROPODA. 
25 
most beautiful and strange forms. They are unprovided with shells 
except in the earliest stages of their existence, when they dwell in a 
minute nautiloid shell, furnished with an operculum, both of which 
Fig. 19. 
The Umbrella-shell (Umbraculum mediterraneum). 
a, shell ; b, gills ; c, tentacles ; d, mouth ; e, foot. 
are subsequently cast off. Unfortunately the colours of these beauti- 
ful creatures cannot be preserved after death, and therefore a small 
series of glass models is exhibited, which will give some idea of 
Fig. 20. 
Naked-gilled Mollusc, or Nudibranch (JDoto coronata). 
a, head ; &, foot ; c, gills ; d, tentacle-sheath ; e, tentacle. 
their great variety in form and colouring. They are found in most 
parts of the world, chiefly in shallow water, but a few species live 
upon floating seaweed in the open sea. Over a hundred species 
exist on the British coast, the majority of which are, however, very 
small. They are chiefly carnivorous, feeding on other molluscs, 
sea-anemones, &c. 
Order 2. — Pulmonata. 
The Pulmonata are furnished with a lung-cavity in place of the Cases 
97—135 
ordinary gill of other Gastropods, and may be termed true air- 
