The Latin for Oyster is _Ostrea_, and that is a name given to a genus of the _Pectinidæ_ family, comprising beside the _O. edulis_, or Common Oyster, many other species. _Edulis_ means eatable. Home naturalists divide these Ostraceans into two groups, first with simple or undulated, but not plaited valves; second, those which have the borders of their valves distinctly plaited. To the first group belong the Common Oyster, and between thirty and forty other living species which are found principally in warm and temperate latitudes. In the Polar ocean none have been discovered, and in the hotter climates they are most abundant, being found in large beds or banks near the coast, and often attached to rocks and even to trees which grow by the water, so that the accounts of some old travellers who stated that they saw Oysters growing upon trees, were not so false as many supposed them. [Illustration] [Illustration] The annexed figure is that of the Cock’s-comb Oyster, _Ostrea Crista-Galli_, a native of the Indian Seas, and a very remarkable shell, on account of its crooked or deeply indented form; the specific name means cock’s-crest. The Chinese Window Oyster, called _Placuna Placenta_, which we may, if we like, translate into a pleasant or agreeable cake; the shell, it will be seen, is round like a cake, and its smoothness and regularity of form render it agreeable to look upon; this species too comes from the Indian Seas, where it is taken on sandy bottoms. The American Spiny Oyster, or _Spondylus Americanus_, brings us into another family, that of the Water Clams, called by naturalists _Spondylidæ_; with the spines stuck out every way, and no way in particular, it looks like a head of hair greatly in need of the assistance of one of its _pectinated_ relatives. The specific name of this curious shell explains itself; the generic name comes from the Latin _Spondylis_—a kind of serpent. [Illustration]