Isopods, a group of 14-footed crustaceans, so called because their thoracic feet, the three anterior in one series and the four posterior in another, are nearly equal; the branchiae are six pairs and abdominal. Some inhabit the sea, where they are generally parasitic on other animals; others are terrestrial, living in dark and damp places, like the wood lice and sow bug. The eyes are sessile or not placed upon stalks, and the head is distinct from the segment bearing the first pair of feet.
Issaquena, a W. county of Mississippi, bounded W. by the Mississippi river and S. E. by the Yazoo, which is navigable by steamboats; area, 720 sq. m.; pop. in 1870, 6,887, of whom 6,146 were colored. It is drained by Big Sunflower river, Deer creek, and Steel's bayou, and has a low and level surface, portions of which are often inundated. The.soil is rich. The chief productions in 1870 were 82,825 bushels of Indian corn, 5,105 of sweet potatoes, and 15,821 bales of. cotton. There were 562 horses, 931 mules and asses, 619 milch cows, 1,559 other cattle, and 1,675 swine. Capital, Tallulah.
Issoire, a town of Auvergne, France, in the department of Puy de-Dome, at the confluence of the Crouze and the Allier, 81 m. W. S. W. of Lyons; pop. in 1866, 6,294. It has a fine church of the 11th century, a college, copper works, and an active trade.
Issoudun, a town of Berry, France, in the department of Indre, on the river Theols and on the railway from Orleans to Limoges, 22 m. S. W. of Bourges; pop. in 1866, 14,261. It contains the ruins of a castle built in the 12th century, and has four churches, a theatre, manufactories of cloth and faience, and an important trade in corn and wine.
Issus, an ancient town of Cilicia, in Asia Minor, at the head of the gulf of Issus, celebrated for the battle fought near it in 333 B. C, in which Alexander the Great defeated Darius. Its exact site is uncertain. The battle also between the army of Septimius Severus and Niger (A. D. 194) was fought near Issus.
Istapa, Or Istapam, a port on the Pacific coast of Guatemala, in Central America, in lat. 13° 53' N., Ion. 90° 43' W., at the mouth of the river Michatoyat. Alvarado here built the vessels in which he sailed against Pizarro and Almagro in Peru, in 1533. It remained the only port of Guatemala on that side of the continent till 1853, when it was abandoned for a point called San Jose, 12 m. N., which was supposed to have fewer disadvantages. Both Istapa and San Jose, however, are entirely open to the sea, and vessels are unable to approach nearer than 1 1/2 m. from the shore, where they are obliged to anchor on a bottom of shifting sands, prepared to stand out to sea at a moment's warning.
Itacolumite (from Itacolumi, a mountain of Brazil), a granular silicious rock, of laminated structure, found with talcose slates and more or less intermixed with talc or with mica. It is distinguished by its peculiar flexibility, sheets of it bending back and forth as if jointed within. It is of particular interest from its occurrence at the localities in the gold regions where diamonds are found. It is met with in Brazil, the Ural mountains, and in Georgia and North and South Carolina. In the last named state Mr. Oscar Lieber has observed the passage of the itacolumite into a true sandstone or a conglomerate, proving its sedimentary origin.