PNEUMONOBRANCHIATA. 49 



phragm formed of its inspissated humours, and some- 

 times hardened with a little calcareous matter. 



These animals are all hermaphrodite, but require 

 mutual impregnation, and feed on vegetables; but 

 some few have carnivorous propensities, and others, 

 when they live near man, acquire bad habits, and 

 eat paper and dead animal matter. 



They may be divided into groups, according to 

 the structure of the mouth, and the form of their 

 tentacles, which conform to their more or less aquatic 

 habits. 



This order is divided into four sub-order's, in the 

 following manner : 



I. PETROPHILA. Eyes at the end of an elongated 



contractile peduncle ; tentacles flat, contractile ; 

 jaws none ; organs of generation far apart, 

 apertures united by a lateral groove ; teeth flat, 

 four-sided, close, side by side; shell none, as 

 Onchidiadce. 



II. GEOPHILA. Eyes at the end of an elongated 



retractile peduncle ; tentacle cylindrical, re- 

 tractile, sometimes wanting ; organs of gene- 

 ration in a common cavity ; operculum none. 

 Terrestrial. 



1. Lumbricivora. Mouth proboscis-like ; jaws 

 none; teeth slender, conical, distant. Carni- 

 vorous, subterraneous, as Testacellidce. 



2. Phyllivora. Mouth prominent; jaws one or 

 two, distinct ; teeth four-sided, flat, with a re- 

 curved tip, close together, side by side; her- 

 bivorous, as Arionida and Helicidce. 



