Page:The American Cyclopædia (1879) Volume XV.djvu/898

 TRILOBITE TRINCOMALEE ing it, becoming more delicate toward the median line ; between the two is found in the fossils a stony layer measuring their distance from each other ; the lower surface was soft and membranous; the skin was undoubtedly cast as in other articulates, and Wahlenberg has suggested that some supposed new species may have been founded on their cast shells. They have been divided into three families, according to the nature of their covering : 1, eurypteridce, without shell, including the single genus eurypterus (De Kay) ; 2, cytherinidce, with bivalve, bean-shaped shell, including the single genus cytherina (Lam.) ; and 3, trilo- fiita, with a shell having as many rings as there are joints to the body, containing many genera and species, and divided into two large groups, one with the power of rolling into a ball, like calymene, and the other with no such power, as in ogygia. According to Bur- meister, the trilobites moved on- ly by swimming, just below the Caiymene. surface of the water, with the back downward, rolling into a ball when danger threatened from above, and did not creep upon the bottom ; they lived in shallow water, near the coast, associating in immense numbers, chiefly of the same species ; while only six or eight species occur in a given stratum, the number of individuals was very great ; their food consisted of small aquatic an- imals and their spawn ; they underwent pro- gressive metamorphoses, and varied considera- bly according to age ; their metamorphoses are given at length by Barrande, who makes four distinct types, according to the serial develop- ment of the different parts. Trilobites are among the oldest of the articulata; though none are now living, during the palaeozoic pe- riod they were very abundant, and almost the only representatives of their class. They have been most studied in Bohemia, and by M. Bar- rande. None are found above the carbonif- erous rocks, and only two or three in them. Barrande's primordial fauna, or the lower Si- lurian, has one genus but no species passing to his second fauna or middle Silurian, and this has many genera but no species common to it and the third fauna or upper Silurian, which in turn has several genera passing to the Devo- nian fauna the whole series affording remark- able proofs of the limitations of faunas in time ; the distribution of particular genera and species in space was also very circumscribed, probably on account of their feeble locomotive powers. In America several trilobites, espe- cially paradoxides and its allied genera, have been met with in slates formerly classed among the metamorphic rocks, as the P. Harlani (Green), found in Braintree, Mass., in 1856, by Prof. W. B. Rogers, and this and other tri- lobites found in Canada and Newfoundland. The trilobites have long attracted much inter- est, as well on account of the great numbers in which they have been found in many locali- Paradoxides Harlani. ties, as from their singular conformation, and the perfect state in which their forms are pre- served. The eye is very beautiful, and its per- fection in many of the stony fossils, especially some brought from the Hartz moun- tains, and from the upper Silurian lime- stone of Dudley, England, is very re- markable ; the fa- cets or lenses, some- times nearly 400 in number, are like those observed in the eye of the dra- gon fly and butter- fly, and as in these insects are arranged around a conical tube through which the visual rays enter from almost every direction ; in the asaphus caudatus each eye thus has a range of nearly three fourths of a circle, and both together command a panoramic view. The structure of the eye also indicates the prevalence in those ancient periods of the same conditions of the waters and the atmosphere, as regards their adaptation to the organs of vision, as now obtain. The geographical range of trilobites is very extensive; these fossils are met with at most distant points, both of the south- ern and northern hemispheres ; they are found all over northern Europe, and in numerous localities in North America, in the Andes of Bolivia, and at the Cape of Good Hope. Tren- ton Falls, N. Y., has afforded, in the limestone known by its name, fine specimens of the spe- cies calymene Blumeribachii (Brongn.). Leba- non, Ohio, is another interesting locality. In Adams co., Ohio, Dr. Locke procured an iso- telus, to which he gave the specific name me- gistos, that measured more than 20 in. in length and 12 in. in width ; the /. gigas and paradox- ides Harlani have been found more than 12 in. long. (See " American Journal of Science," 1871, p. 228, and 1872, p. 268.) TRIMBLE, a N. county of Kentucky, border- ing on the Ohio river ; area, 150 sq. m. ; pop. in 1870, 5,577, of whom 456 were colored. The surface is generally hilly and the soil fer- tile. The chief productions in 1870 were 31,- 848 bushels of wheat, 209,060 of Indian corn, 38,216 of oats, 12,647 of potatoes, 658,465 Ibs. of tobacco, 10,676 of wool, 24,370 of but- ter, and 1,268 tons of hay. There were 1,906 horses, 1,064 milch cows, 1,882 other cattle, 3,043 sheep, and 6,512 swine. Capital, Bedford. TRINCOMALEE, a town of Ceylon, in the N. E. part of the island, in lat. 8 34' N., Ion. 81 12' E. ; pop. about 20,000. It stands on the N. side of the entrance to a capacious and se-