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Updated: June 3, 2025
The Crustaceans were plentifully represented by the Trilobites, which appear to have swarmed in the Silurian seas just as crabs and shrimps do in our own; no less than 263 species have been found in the British Silurian fauna.
The eye varies greatly in the number of its lenses, ranging from fourteen in some species to fifteen thousand in others. During the long ages of the Cambrian the trilobite varied greatly. Again and again new species and genera appeared, while the older types became extinct. For this reason and because of their abundance, trilobites are used in the classification of the Cambrian system.
They think of it all as immediate and contemporaneous, a vast panorama of innumerable ages being all crammed for them on to a single mental sheet, in which the dodo and the moa hob-an'-nob amicably with the pterodactyl and the ammonite; in which the tertiary megatherium goes cheek by jowl with the secondary deinosaurs and the primary trilobites; in which the huge herbivores of the Paris Basin are supposed to have browsed beneath the gigantic club-mosses of the Carboniferous period, and to have been successfully hunted by the great marine lizards and flying dragons of the Jurassic Epoch.
M. Barrande pointed out that these primordial trilobites have a peculiar facies of their own dependent on the multiplication of their thoracic segments and the diminution of their caudal shield or pygidium.
Among crustacea, it is very remarkable that trilobites and limulus-like forms are the only representatives of the class during the paleozoic ages; that macrourans prevailed in the same manner during the secondary period; and that brachyurans make their appearance only in the tertiary period.
The trilobites, a quite highly organized order of crustacea, appear in the strata of the silurian epoch almost suddenly, in very many and very distinctly marked species. The uncertainty of our knowledge shows itself most clearly when we ask for the geneologic relationship of the vertebrates. In Chap.
But a complete development, such as already obtains in the lobster, &c., was reached by the Eurypterida and Trilobites of the palæozoic strata; and annelids, probably formed mainly like those of the present day, abounded during the deposition of the oldest fossiliferous rocks.
The Crinoids, with the closed cups in some, and the open, star-like crowns in others, unite features of the present Star-Fishes and Sea-Urchins, and, by their stem attaching them to the ground, include also a Polyp-like character; while the Trilobites, with their uniform rings and their prominent anterior shield, unite characters of Worms and Crustacea.
She asked him no more about trilobites, she did not talk about anything; the subjects the Captain started were soon let drop. And not because she was too ill to talk, for Daisy's eye was thoughtfully clear and steady, and the Captain had no doubt but she was busy enough in her own mind with things she did not bring out. What sort of things? he was very curious to know.
The eyes, dead and turned to stone, were even now regarding him. It was one of the early crustaceans called Trilobites. Separated by millions of years in their lives, Knight and this underling seemed to have met in their death. It was the single instance within reach of his vision of anything that had ever been alive and had had a body to save, as he himself had now.
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