516 NUDIBRANCHS, 
and a secure hiding-place, whither it can retreat during the day, often attains 
an enormous size. 
THe Water Snails are represented by the common POND-SNAIL, or 
Limn@a, shown in the act of climbing up the stem of a water-plant. In 
all the members of this family the shell is thin, and sufficiently capacious to 
contain the entire animal when it desires to_withdraw itself into its home. 
The aperture is simply rounded, without notches or ridges, and the lip is 
sharp. 
It may be found plentifully in nearly all streams where the water is not 
polluted, and the current not very swift. I have genecally found that the 
back eddies of ‘‘lashers” are favourite haunts of various Water Snails. 
DORIS.—(Doris Fohnstoni,) 
WATER SNAIL, —(Limnea stagnalis.) EOLIS.—(Zolis coronata.) 
WE now arrive at a very remarkable series of molluscs which have been 
separated by systematic naturalists into a distinct section, appropriately 
called Nudibranchide, or Naked-gilled Molluscs, because their gills are 
always external and placed on the back or sides of the animals. 
The slug-like animal which is represented crawling on the frond of a 
laminaria, is the common Doris of our own shores. All the members of his 
family to which this creature belongs may be known by the plume-like gills 
set in a circle on the middle of the back, like the feathery coronet with 
