these rivers belong. Some of the species exceed a length of 3 feet. In the United States, where twospecies, Trionyx muticus and Trionyx ferox, occur, the flesh of the latter is said to be most delicate to eat, far surpassing in flavour that of the green turtle. (A. C. G.)
TORTOISESHELL. The tortoiseshell of commerce consists of the epidermic plates of the hawksbill turtle, Caretta imbricata. The plates of the back or carapace, technically called the head, are 13 in number, 5 occupying the centre, flanked by 4 on each side. These overlap each other to the extent of one-third of their whole size, and hence they attain a large size, reaching in the largest to 8 inches by 13 inches, and weighing as much as 9 ounces. The carapace has also 24 marginal pieces, called hoofs or claws, forming a serrated edge round it; but these, with the plates of the plastron, or belly, are of inferior value. The plates of tortoiseshell consist of horny matter, but they are harder, more brittle, and less fibrous than ordinary horn. Their value depends on the rich mottled colours they display a warm translucent yellow, dashed and spotted with rich brown tints and on the high polish they take and retain. The finest tortoiseshell is obtained from the Eastern Archipelago, particularly from the east coast of Celebes to New Guinea; but the creature is found and tortoiseshell obtained from all tropical coasts, large supplies coming from the West Indian Islands and Brazil.
Tortoiseshell is worked precisely as horn; but, owing to the high value of the material, care is taken to prevent any waste in its working. The plates, as separated by heat from the bony skeleton, are keeled, curved, and irregular in form. They are first flattened by heat and pressure, and superficial inequalities are rasped away. Being harder and more brittle than horn, tortoiseshell requires careful treatment in moulding it into any form, and as high heat tends to darken and obscure the material it is treated at as low a heat as practicable. For many purposes it is necessary to increase the thickness or to add to the superficial size of tortoiseshell, and this is readily done by careful cleaning and rasping of the surfaces to be united, softening the plates in boiling water or sometimes by dry heat, and then pressing them tightly together by means of heated pincers or a vice. The heat softens and liquefies a superficial film of the horny material, and that with the pressure effects a perfect union of the surfaces brought together. Heat and pressure are also employed to mould the substance into boxes and the numerous artificial forms into which it is made up.
Tortoiseshell has been a prized ornamental material from very early times. It was one of the highly esteemed treasures of the far East brought to ancient Rome by way of Egypt, and it was eagerly sought by wealthy Romans as a veneer for their rich furniture. In modern times it is most characteristically used in the elaborate inlaying of cabinet work known as buhl furniture. It is also employed as a veneer for small boxes and frames. It is cut into combs, moulded into snuffboxes and other small boxes, formed into knife-handles, and worked up into many other similar minor articles. The plates from certain other tortoises, known commercially as turtle-shell, possess a certain industrial value, but they are either opaque or soft and leathery, and cannot be mistaken for tortoiseshell. A close imitation of tortoiseshell can be made by staining translucent horn. See Comb, vol. vi. p. 178.
TORTOLA.See Virgin Islands.
TORTONA, a town of Italy, in the province of Alessandria, on the right bank of the Scrivia, at the northern foot of the Apennines, 13 miles to the east of Alessandria, was formerly a place of strength until its fortifications were destroyed by the French after Mareugo (1799); the ramparts are now turned into shady promenades. The cathedral, erected by Philip II., is architecturally uninteresting, but contains a remarkably fine Roman sarcophagus. Silk-weaving, tanning, and hat-making are the chief industries; and there is some trade in wine and grain. The population in 1881 was 9023 (commune 14,442).
Dertona is spoken of by Strabo as one of the most important towns of Liguria, and is alluded to by Pliny as a Roman colony. In the Middle Ages it was zealously attached to the Guelphic cause, on which account it was twice laid waste by Frederick Barbarossa (in 1155 and 1163).
TORTOSA, a fortified city of Spain, in the province of Tarragona, and 40 miles by rail to the south-west of that town, is picturesquely situated on the left bank of the Ebro (here crossed by a bridge of boats), 22 miles above its mouth. It is for the most part an old walled town, with narrow, crooked, and ill-paved streets; the houses are lofty, and massively built of granite. The slope on which it stands is crowned with an old ruined castle, com manding a splendid view. The cathedral is a conspicuous building near the river; it occupies the site of a mosque built in 914 by Abd al-Rahman; the present structure, which dates from 1347, has its Gothic character disguised by a classical façade with Ionic pillars and much tasteless modernization. The stalls in the choir, carved by Cristobal de Salamanca in 1588-93, and the sculpture of the pulpits, as well as the ironwork of the choir-railing and some of the precious marbles with which the chapels are adorned, deserve notice. None of the other public buildings, which include an episcopal palace, a town-hall, and numerous churches, require special mention. The manufactures of Tortosa include paper, hats, leather, porcelain, majolica, soap, and spirits. There is an important fishery in the river, and an active trade is carried on through the harbour, which is accessible to vessels of 100 tons burden, corn, wine, oil, wool, silk, fruits, and liquorice (a specialty of the district) being among the leading articles of export. Near Tortosa are rich quarries of marble and alabaster, and the whole surrounding country is very fertile and beautiful. The population within the municipal boundaries in 1878 was 24,057.
Tortosa, the Dcrtosa of Strabo and the Colonia Julia Augusta Dertosa of numerous coins, was a city of the Ilercaones in Hispania Tarraconensis. Under the Moors it became a place of great importance as the key of the Ebro valley. It was taken by Louis the Pious in 811 (after an unsuccessful siege two years before), but was soon recaptured. Having become a haunt of .pirates, and exceedingly injurious to Italian commerce, it was made the object of a crusade proclaimed by Pope Eugenius III. in 1148, and was accordingly captured by Raymond Berengar, assisted by Templars, Pisans, and Genoese. Tortosa fell into the hands of the duke of Orleans in 1708, and was again surrendered in the War of Independence in 1811 to the French under Suchet, who held it till 1814.
