26 CLASS GASTEROPODA. 
or several pieces, but never turbinated or operculated. Their 
gills are attached under the reflected edges of their mantle, as 
in the inferobranchiata. 
THE FIRST ORDER OF GASTEROPODA. 
THE PULMONARIA 
Are distinguished from the other mollusca in respiring the 
elastic air through an open hole under the reflected edge of ° 
the mantle, which they dilate or contract at pleasure. Accord- 
ingly, they have no gills, but merely a net-work of pulmonary 
vessels, which spread over the parietes, and principally over 
the roof of their respiratory cavity. 
Some are terrestrial, others live in the water, but are obliged 
from time to time to come to the surface to open the orifice 
of their pectoral cavity to respire. 
All these animals are hermaphrodites. 
The TERRESTRIAL PULMONARIA 
Have almost all four tentacula; two or three only, of very 
small size, do not show the lower pair. 
Those among them which have no apparent shell, formed in 
Linneus the genus 
Limax, L., 
Which we divide as follows: 
LimMAxX (proper), 
Have the body elongated, and for a mantle a fleshy compact 
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