6 ? 
periwinkle. The likeness is further strengthened by the presence of 
a hard horny covering, known as the operculum or cap, which 
exactly fits the opening of the shell, and protects the more delicate 
parts within. If one of these snails be dropped into an aquarium, 
after it has satisfied itself that danger is past, it will slowly put out 
its two very winkle-like horns, and begin crawling over the stones in 
search of food. When in this position it is quite easy to see to 
which portion of the animal the operculum is attached. It is 
carried, as in winkles, whelks, and all the marine univalves 
possessing one, immediately behind the shell, so curiously enough 
this snail carries its cap on its tail. 
Ramshorn Snail. — This water mollusc is common in almost 
every pond and stream in Britain, and has a special taste for de- 
caying vegetation. A dozen or so of these snails should be kept in 
every fair sized aquarium, as they will do good service in removing 
small bits of rotting waterweed, which if left would discolour the 
water and render it foul. The shell is usually covered with a green 
water growth in ihe larger specimens, but if this is cleaned off the 
real colour will be found to be a shining chocolate brown. Their 
eggs which are enclosed in elliptical jelly-like cases, are fixed to 
vyater plants. 
Freshwater Whelk. — One of the very first creatures to make 
the acquaintance of the pond hunter is this snail. It seems to be 
very common in most waters in the south of England, but its 
favourite haunts are weedy ponds. In such situations numbers 
may often be seen swimming in an inverted position on the sur- 
face of the water. The eggs are laid on submerged portions 
of aquatic plants in long jelly-like capsules. In a few weeks the 
tiny snails make their appearance and wander off in search of 
food. This consists of vegetation chiefly, but the full-grown mol- 
luscs will readily become carnivorous. In an aquarium of the 
writer six of these mature whelks cleaned off every shred of flesh 
from a dead young roach, which was quite three inches long, and 
this they managed in less than a fortnight. 
CRUSTACEANS. 
River Crayfish. — To obtain these crustaceans we must go down 
to the banks of some river towards dusk. If the stream be a likely 
one numbers of crayfish will be seen sallying forth from their holes 
in the banks hunting for food. Frequently they may be met with 
during the day, but, as they are essentially nocturnal in their habits, 
they are far more likely to be found towards evening. The crayfish 
is a member of the family to which the lobster belongs, and is pro- 
tected in the same way by a horny covering. This armour is formed 
of a very tough skin made still harder by the deposition of chalk. 
This is supplied in the substance of the water weeds which form a 
large portion of the diet of this animal. We should expect, then, 
to find crayfish in rivers whose waters contain a certain amount of 
calcarious substance, as, for the reason just stated, they will not 
thrive in streams which do not flow through chalky districts. To 
keep these creatures healthy in aquaria, an almost constant supply 
of water must be maintained, for, if not, they become limp and 
sluggish, and very soon die. They will partake of almost anything 
in the way of meat and vegetables, but, of course, small pieces of 
fish and water weeds will suit them best. All the food not eaten 
will, if not removed, cause the fouling of the water and the death of 
the crayfish. A shallow vessel well supplied with heaps of big 
stones, under and among which they can hide, will also be good 
for their health. 
