18 LAND AND FRESH-WATER MOLLUSKS. 
Limax arsorum—(the Tree Sluq) (Pl. V., fig. 
33).—This arboreal species bears a consider- 
able resemblance to the young of L. maximus, 
from which it may be distinguished by the 
upper tentacles being much shorter, in pro- 
portion, than those of that species, and in 
the less pointed hinder margin of the shield. 
In colour it is greyish, spotted with yellow- 
ish-white, with a central dusky stripe and a 
darker band on each side. The back rounded, 
carinated at the tail; the shield wrinkled, and 
pointed behind; upper tentacles short. The 
length of the body nearly three inches. The 
shell is oval, thin, nearly flat. 
This species is not well known, and its apparent. 
rarity is due to its bemg mistaken for the young 
of L. maximus. Its habitats are, however, not 
those of that species. Jt lives on trees, especially 
the beech, and those that are decaying, feeding 
on the wood. It also may be found under stones, 
and under fallen trunks in woods, or even upon 
bare rocks. Like some other slugs, the young 
descend from the branches of the trees by threads 
of slime. This species has been met with through- 
out Great Britain by several critical observers, 
though generally absent from local lists of 
species. 
The capability of this species of letting itself 
down from a height to the ground by the tenacity 
