SHELDON 383 SHELL newspaper, and was the author of numer- ous books including "His Brother's Keep- er," "In His Steps," "Malcolm Kirk," "Edward Blake," "Born to Serve," etc. In 1920 he was appointed editor of the "Christian Herald," New York. SHELDON, EDWARD BREWSTER, an American playwright, born in Chicago, in 1886. He graduated from Harvard University in 1907 and at once began the writing of plays. Among those were successfully produced "Salvation Nell" (1908) ; "The Nigger" (1909) ; "The High Road" (1912); "Garden of Para- dise" (1915). SHELDRAKE, in ornithology, the Tadorna cornuta (or vulpanser) of mod- ern ornithologists; Anas tadorna. It is somewhat larger than an ordinary duck, with a fleshy protuberance at the base of the bill, whence its specific name. It is a very handsome bird; head and upper neck dark, glossy green, broad white col- lar, below which a broader band of bright SHELDRAKE bay extends from the back across the breast; outer scapulars, primaries, a me- dian abdominal stripe, and a bar on tip of middle tail quills black; inner secon- daries and lower tail coverts gray; specu- lum rich bronze green; rest of plumage white. The female is smaller and less brilliantly colored. It frequents sandy coasts in Europe and North Africa, rang- ing across Asia to Japan ; nesting usually in a rabbit hole. The ruddy sheldrake, T. casarca, is a native of Barbary, south- eastern Europe, and Central Asia. Its color is an almost uniform bay, the male with a black ring round the neck. The common sheldrake breeds freely in cap- tivity. SHELL, in zoology, the hard calcareous substance which either protects the testa- ceous mollusca externally, or supports certain species of them internally. Though shells, properly so called, which form the habitation of testaceous animals are sometimes confounded with the shelly coverings which protect the Crustacea (crabs and their numerous allies), a very obvious and striking difference exists be- tween them, as well as between the kinds of animals which respectively inhabit them. The shells of testacea are com- posed of carbonate of lime, combined with a small portion of gelatinous mat- ter; they are, in general, permanent cov- erings for their inhabitants; and the animal is of a soft substance, without bones of any kind, and attached to its domicile by a certain adhesive property. On the other hand, those animals which are defended by a crustaceous covering cast their shells and renew them annu- ally; while the animals themselves are of a fibrous texture, with articulated limbs, and protected, as it were, by a coat of mail. Shells are divided into Multivalves, Bi- valves, and Univalves. The first order, Multivalve, is made up of shells consisting of more shelly parts or pieces than two. The second order, Bivalve is made up of shells having two parts or valves, gen- erally connected by cartilage or hinge; as in the cockle and mussel. The third order, Univalve, is made up of shells complete in one piece — as in the peri- winkle and the whelk — and they are sub- divided into shells with a regular spire, and those without a spire. The shells composing this order are far more nu- merous than those of the two preceding, both in genera and species. The spire is a prominent feature of the Univalve; and on its being lengthened or elevated, shortened or depressed, etc., depends much of the generic and specific definitions. Shells increase in size by the deposition of new layers internally on those already formed. Each new layer extends more or less beyond the margin of the layer to which it is applied, so that as the ani- mal becomes older its shell becomes larger and thicker. The outer surface is gen- erally covered by a thin layer of mem- branous or horny matter, named the epi- dermis, and the inner surface is often covered with a layer of a pearly nature. In military usage the name shell is given to a hollow vessel of metal contain- ing gunpowder, or other explosive com- pound, so arranged that it will explode at a certain point and spread destruction around by the forcible dispersion of its fragments. The invention of this missile, formerly called a Bomb (q. v.), cannot be accurately traced. Shells were em- ployed in a. D. 1480 by the Sultan of Gujerat, and by the Turks at the siege of Rhodes in 1522. The Spaniards and Dutch both used them during the war
