o dry up. The big ones
must be killed in boiling water, when the animal can be pulled out
with a hook made of a crooked pin, leaving the shell clean and
perfect. The slugs are not attractive on account of the slime which
they throw out and can only be kept in spirits. Some of the species
found in California are as large as a small cigar, but those of the
states east of the Rocky Mountains are smaller and have mostly been
introduced from Europe, where they do a lot of mischief by eating such
garden plants as lettuce.

Many of the fresh-water snails are abundant in brooks and ponds, and
their relations, the fresh-water mussels, are often very numerous in
shallow rivers. They have a shell frequently beautifully pearly, white
or purple, and sometimes have the brown outer skin prettily streaked
with bright green.

[Illustration: Fig. 2 Whelk (Buccinum umatum)]

[Illustration: Fig. 3 Pond snail (Lymnaea palustris)]

The principal fresh-water snails are the pond snail (_Lymnaea_; see
Fig. 3); the _Physa_ (see Fig. 6), which is remarkable for having the
coil turned to the left instead of the right; and the orb-snail,
(_Planorbis_: see Fig. 4) which has its coil flat. All of {96} these
lay minute eggs in a mass of transparent jelly, and are to be found on
lily pads and other water plants, or crawling on the bottom, while the
mussels bury themselves more or less in the mud or lie on the gravelly
bottom of streams. There is also a very numerous tribe of small
bivalve shells, varying from half an inch to very minute in size,
which are also mud lovers and are known as Sphaerium or Pisidium,
having no "common" English names, since only those who hunt for them
know of their existence.

On the seashore everybody knows the mussel (Mytilus: see Fig. 5), the
soft clam, the round clam, and the oyster, as these are sought for
food; but there is a multitude of smaller bivalves which are not so
well known. The sea-snails best known on the coast north of Chesapeake
Bay are the whelk (Buccinum: see Fig. 2), the sand snail or Natica,
which bores the round holes often found in clam shells on the beach,
in order to suck the juices of its neighbors, and the various kinds of
periwinkles (rock snails or Littorina) found by the millions on the
rocks between tides. These, as well as the limpets, small boat-shaped
or slipper-shaped conical shells found in similar places, are
vegetable feeders. Altogether, there are several hundred kinds foun