ICOSAHEDRON (Gr. εἴκοσι, twenty, and ἕδρα, a face or base), in geometry, a solid enclosed by twenty faces. The “regular icosahedron” is one of the Platonic solids; the “great icosahedron” is a Kepler-Poinsot solid; and the “truncated icosahedron” is an Archimedean solid (see [Polyhedron]). In crystallography the icosahedron is a possible form, but it has not been observed; it is closely simulated by a combination of the octahedron and pentagonal dodecahedron, which has twenty triangular faces, but only eight are equilateral, the remaining twelve being isosceles (see [Crystallography]).
ICTERUS, a bird so called by classical authors, and supposed by Pliny to be the same as the Galgulus, which is generally identified with the golden oriole (Oriolus galbula).[1] It signified a bird in the plumage of which yellow or green predominated, and hence Brisson did not take an unhappy liberty when he applied it in a scientific sense to some birds of the New World of which the same could be said. These are now held to constitute a distinct family, Icteridae, intermediate it would seem between the [Buntings] (q.v.) and [Starlings] (q.v.); and, while many of them are called troopials (the English equivalent of the French Troupiales, first used by Brisson), others are known as the American [Grackles] (q.v.). The typical species of Icterus is the Oriolus icterus of Linnaeus, the Icterus vulgaris of Daudin and modern ornithologists, an inhabitant of northern Brazil, Guiana, Venezuela, occasionally visiting some of the Antilles and of the United States. Thirty-three species of the genus Icterus alone, and more than seventy others belonging to upwards of a score of genera, are recognized by Sclater and Salvin (Nomenclator, pp. 35-39) as belonging to the Neotropical Region, though a few of them emigrate to the northward in summer. Cassicus and Ostinops may perhaps be named as the most remarkable. They are nearly all gregarious birds, many of them with loud and in most cases, where they have been observed, with melodious notes, rendering them favourites in captivity, for they readily learn to whistle simple tunes. Some have a plumage wholly black, others are richly clad, as is the well-known Baltimore oriole, golden robin or hangnest of the United States, Icterus baltimore, whose brightly contrasted black and orange have conferred upon it the name it most commonly bears in North America, those colours being, says Catesby (Birds of Carolina, i. 48), the tinctures of the armorial bearings of the Calverts, Lords Baltimore, the original grantees of Maryland, but probably more correctly those of their liveries. The most divergent form of Icteridae seems to be that known in the United States as the meadow-lark, Sturnella magna or S. ludoviciana, a bird which in aspect and habits has considerable resemblance to the larks of the Old World, Alaudidae, to which, however, it has no near affinity, while Dolichonyx oryzivorus, the bobolink or rice-bird, with its very bunting-like bill, is not much less aberrant.
(A. N.)
[1] The number of names by which this species was known in ancient times—Chloris or Chlorion, Galbula (akin to Galgulus), Parra and Vireo—may be explained by its being a common and conspicuous bird, as well as one which varied in plumage according to age and sex (see [Oriole]). Owing to its general colour, Chloris was in time transferred to the Greenfinch (q.v.), while the names Galbula, Parra and Vireo have since been utilized by ornithologists (see [Jacamar] and [Jacana]).
ICTINUS, the architect of the Parthenon at Athens, of the Hall of the Mysteries at Eleusis, and of the temple of Apollo at Bassae, near Phigalia. He was thus active about 450-430 B.C. We know little else about him; but the remains of his two great temples testify to his wonderful mastery of the principles of Greek architecture.