66 LAND AND FRESH-WATER MOLLUSKS. 
The Iyoprrcutata, or typical Pulmonifera, are 
naturally divided into the slugs, land snails, and 
water snails; and are embraced in the following 
famihes :— 
1 { Animal slug-like cea wines. Seas er 
Ate » contained in a more or less spiral shell... 3 
> § Mantle small, shield-like ... ... ... Limacide 
“sity » enveloping the body... ... ... Oncidiade 
. § Two pairs of retractile tentacles ... ... Felicide 
” ) Tentacles two, eyes sessile ee 
4 { Animal aquatic, aperture of shell edentulous, Limneide 
‘ / Aperture of shell toothed ... ... ... Auriculide 
Stues (Famity Limacipz). 
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 
