. A prettily formed snail of medium size, of somewhat flattened shape, with attractive brown markings on a horn-colored background. One of the better ones, a good scavenger and one that won't attack aquatic plants. If you breed snails, include this one, for it is easy and quite useful. Every time you clean your pool you will find empty shells of this species, for it is comparatively short-lived.

. One of the smaller species, with a conch-shaped shell, bright orange-red. Very useful, of average hardiness, and reproduces in pool or aquarium without special conditions.

. Also called Great Japanese Snail, Trapdoor Snail. One of the largest and one of the best scavengers, often grows to the size of a golf ball, is very hardy, and has a long life. The pea-sized progeny are born alive, too big for fish to eat.

. Scavengers. Mussels can be ordered from practically any dealer, or you can dig your own. Find a stretch of river shore strewn with mussel shells, and draw a rake through the mud and sand of the nearby shallows until you turn up as many as you want.

. Resembles the Japanese Snail except for three brown stripes running parallel to the spiral of the shell, and sometimes sold as such, but is far inferior. Practical1y inactive, and does little good.

. Small snail about the size of a match head, with flat, semitransparent shell, rather attractive. Turns up occasionally in pools and aquariums, sometimes in considerable number, having apparently gotten there as a stowaway on some newly purchased aquatic plant. Do what you like with limpets, for they are as harmless as they are useless.

. Small, dark snail hardly as large as the end of a little finger. Easily identified because the spiral of the shell is the reverse of that of most other snails, might be called "the snail with the left-hand thread." Breeds prolifically, and the hard shells of the very young protect them from fish. Called the best of al1 the scavengers, a busy and thorough feeder. The small size enables it to move easily among the more slender plant stems in search of algae, feeding locations that other snails are usually too large and too heavy for.

Also called Coral Snail, Copenhagen Red Snail. An excellent scavenger with a large, flattened, orange-red shell shaped like the horn for which it is named. Does quite well in pools, but is particularly popular for aquariums, where it can be seen. Considered the most handsome snail.

Black-shelled, medium-sized snail, similar in shape to the Red Ramshorn and just as good a scavenger. Quite common in European water gardens and aquariums, but somewhat scarce in the United States.

. Similar to the Black Ramshorn, but with a white shell. Common in Europe, comparatively rare in the United States.

. Two or three of these to every 10 gallons of water in an aquarium can do a great deal of good, for they live by extracting algae and other bits of living matter from the water around them. In an outdoor pool their use is questionable, for they die easily, and as they decompose they foul the water unless quickly consumed by snails. Dead mussels can quickly be spotted in an aquarium and removed, but in a pool, where several dozen of them would be required to do any good, they can easily decompose unnoticed. Even in an aquarium they are subject to some criticism, for they move ponderously, roiling the water and often uprooting aquatic plants.