The distinguishing marks of shells are the number of parts of which they are composed, and their peculiar forms and prominences. Some consist of a single piece, some of two pieces, and some of three. The textures of shells are described as pearl, fibrous, horny, and some are glassy and translucent. The pearly shells are in alternate layers of very thin albuminous membrane and carbonate of lime, which by their minute undulations give the pearly lustre. This structure is the least permanent and in some geological formations the shells that were provided with it have disappeared, leaving only their casts, while those of fibrous texture are preserved unchanged. Colors, however beautifully exhibited upon the surface of shells, are to them no more distinctive features than to the minerals and flowers upon which they are also prominently displayed. They are most richly developed upon those surfaces most exposed to the light and in the class of shells found in shallow waters. The whole number of species of molluscous animals known is estimated at about twelve thousand recent and fifteen thousand fossil. Many of the living species furnish wholesome food, and some are esteemed as delicacies. The marine shells, by the immense numbers in which they are produced, perform an important office in abstracting from the sea-water its excess of calcareous matter and thus aid in maintaining its purity. As objects of beauty, shells have always been admired and frequently been used as ornaments. Some varieties were used by the Athenians as ballots, with the name upon them of the person to be banished, whence the term ostracism. Some shells have served the purpose of coin among rude nations. Others are noted for the pearls which are secreted between their valves around some foreign substances. Mother-of-pearl is the polished shell of nacreous. Rare species of shells are highly prized by collectors, and single specimens have been sold for large sums. The South Sea Islanders use the conch as an instrument of music, blowing into the shell through the broken top, thereby producing a loud and mellow sound. It is a species of sea conch which is represented by the god Triton. In many rural parts of the United States conches are used in place of dinner bells or tin horns to call persons from a distance. THE FLOWN BIRD. R. H. STODDARD. The maple leaves are whirled away, The depths of the great pines are stirred; Night settles on the sullen day As in its nest the mountain bird. My wandering feet go up and down, And back and forth, from town to town, Through the lone woods and by the sea, To find the bird that fled from me. I followed, and I follow yet, I have forgotten to forget.