05 
CHAPTER IY. 
AIR-BEE A THING SNAILS. 
Class Pulmonieera. 
T HIS class embraces all the land snails, land 
slugs, and sucIl of the water snails which 
breathe air : they are closely related to Paludina , 
and to the plant-eating sea snails. Their breathing 
organ is the simplest form of lung, formed by 
the folding of the mantle, over which the blood¬ 
vessels are distributed, and occupies the same 
position as the branchial chamber of Paludina , 
&c. This chamber opens externally by a round 
contractile aperture on the margin of the mantle 
over the neck, on the right side. There is no 
special mechanism of respiration. The functions 
of both sexes are united in each individual. The 
Pulmonifera vary much in appearance and habits. 
The form and number of teeth on the lingual 
ribbon afford good characters for the distinction 
of genera and families, as also for the separation 
of allied species. The class is divided into two 
orders,— Inoperculata, without an operculum, and 
Operculata , possessing an operculum. 
E 
