66 
LAND AND EEESH-WATER MOLLUSKS. 
The Inoperculata, or typical Pulmonifera, are 
naturally divided into the slugs, land snails, and 
water snails; and are embraced in the following 
families :— 
j {Animal slug-like .. ... 2 
( „ contained in a more or less spiral shell... 3 
2 | Mantle small, shield-like . Limacidw 
l „ enveloping the body.. ... Oncidiadce 
g ( Two pairs of retractile tentacles. Helicidce 
\ Tentacles two, eyes sessile . 4 
^ j Animal aquatic, aperture of shell edentulous, Limnceidce 
( Aperture of shell toothed . Auriculidw 
Slugs (Family LiMAcmaa). 
Slugs are very conspicuous among the mollusca, 
and readily recognized by their elongated, more 
or less naked bodies. The body is united in its 
whole length with the foot beneath; the head 
is furnished with four cylindrical tentacles, and 
eyes are situated on the upper pair. The slugs 
resemble in many respects the snails, and are 
regarded by the vulgar as such, which have the 
peculiar power of leaving their shells during the 
summer and retiring to them again for protection 
on the approach of winter; so that, if this were 
true, we ought only to find snails during one 
season and slugs during another. But the snail 
cannot leave its shell, being attached to it by 
muscles. There are many points of difference 
