as evidenced in the construction of the most humble creatures. The winkles accomplish for the marine-tank what the fresh-water snails do for the river-tank, they scrape confervoid growths from the glass, and so help to preserve the crystalline aspect of the tank. All the species of winkle are capable of domestication, Littorina littorea, the commmon sort, and E. littoralis, a pretty little fellow, with a gaily mottled hybernaculum.
PORCELLANA PLATYCHELES, CANCER PAGURUS.
The Trochus tribe, better known as Tops, are also useful as cleaners, and in appearance are more stately and ornamental than the winkle, their cleanly marked conical shell attracting as much attention from strange eyes as the noble planorbis comeus does in the river-tank. Generally speaking, univalves are more easily kept than bivalves; many of the latter are apt to die off, and cause some amount of putrescence before their demise is discovered.
