18 CONCHOLOGIA CESTRICA. 



Order PULMONIFERA. 



Terrestrial, or sub-aquatic animals, which respire free 

 air, through an opening in or under the right side of the 

 mantle. In some of the families of this order, the animal 

 is furnished with a testaceous or horny plate, the opercu- 

 lum, attached to the posterior part of the foot When 

 the animal retires within the shell, the posterior half of 

 the body is folded on the anterior, resembling in its 

 action the shutting of a clasp-knife, after which, the head 

 and body are withdrawn, leaving the operculum, which 

 is situated on the posterior part of the foot, to close the 

 aperture. 



Sub-order GEOPHILA. 



Animal, terrestrial, tentacles four, retractile by inver- 

 sion, or contractile with the head beneath the mantle ; 

 upper pair long, cylindrical, ending in bulbs, which con- 

 tain the eyes ; lower ones short, or obsolete ; shell mostly 

 spiral. 



INOPERCULATA. 



The operculum wanting. 



Family PHILOMYCENID^E. 



The Slugs. 



Mantle covering the entire upper surface of the animal. 

 Shell entirely wanting. 



DIAGRAM OF THE GENERA AND SPECIES OF THE FAMILY PHILO- 

 MYCENID^:. 



FAMILY, f GENUS, TEBENNOPHORUS. f SpECIES Carolinensis, 



PHILOMYCENID^E. t SUB-GENUS, PALLIFERA. -I ' ' dorsalis. 



OBS. The slugs, or naked snails, have many charac- 

 ters common to the true snails ; both are nocturnal in 



