ESTHE'RIA (Neo-Lat., anagram of Saint A bivalve phyllopod crustacean of the order Branchiopoda, found in a fossil state in deposits of fresh and brackish water origin, from the Devonian to the Pleistocene. The animal is lilt well segmented. and is able to withdraw itself wholly within its shell. (For its anatom ical characters, see the articles on and Pitym.oronA.) The shell varies in size from one-eighth to one inch in length, and is of round ed, flattened form, with moderately prominent beaks near the hinge-line. In texture it is thin and inembranaceous, and the surface is usually marked by concentric folds or imbricating ridges between which are trellised or anastomosing lines. This latter character serves to distinguish Esthe ria shells from the shells of small pelecypods such as Posidonomya. One species ( Estheria membrana•ett) is found in the Old Bed Sand stone of the British Devonian, in equivalent beds of Germany, and in the contempora IIPMIS forma tions of the Oneonta-Castkill group of New York State. About twenty-four living species of Esthe
ria, and about an equal number of fossil species, are known from widely distributed regions. Al lied genera are Limnadia and Limnetis, each rep resented by a few species, and the fossil genus Leaia, found in the Carboniferous and Permian formations, which differs from Estheria in the presence of diagonal ridges that run from the umbones to the ventral margins of the shell.
BIBLIOGRAPHY. Jones, “A Monograph of the Bibliography. Jones, “A Monograph of the Fossil Estheri:e," Monographs of the Palmonto graphical Society (London, 1862) ; "On Fossil Estherife and Their Distribution," Quarterly Journal of the GeOlogical Society of London, vol. Nix. (London, 1863). See also CRUSTACEA P Y LLOPODA , and, for illustration, see Plate of P YLLOPODA.