(Also see [Part IV].)
Illustrated: Matthew, Amer. Jour. Sci., vol. 46, 1893, pl. 1, figs. 1-7;—Trans. N. Y. Acad. Sci., vol. 12, pl. 8, figs. 1-7.—Beecher, Amer. Jour. Sci., vol. 46, 1893, text figs. 1-3;—Amer. Geol., vol. 13, 1894, pl. 3;—Amer. Jour. Sci., vol. 47, pl. 7, text fig. 1;—Amer. Geol., vol. 15, 1895, pls. 4, 5;—Ibid., vol. 16, 1895, pl. 8, figs. 12-14; pl. 10. fig. 1;—Amer. Jour. Sci., vol. 1, 1896, pl. 8; Geol. Mag., dec. 4, vol. 3, 1896, pl. 9;—Eastman-Zittel Text-book of Paleontology, vol. 1, 1900, text figs. 1267-1269;—2d ed., 1913, fig. 1375; Studies in Evolution, 1901, reprint of all previous figs.;—Amer. Jour. Sci., vol. 13, 1902, pl. 2, figs. 1-5; pl. 3, fig. 1; pl. 4, fig. 1; pl. 5, figs. 2-4;—Geol. Mag., dec. 10, vol. 9, 1902, pls. 9-11, text figs. 1-3.—Walcott, Proc. Biol. Soc. Washington, vol. 9, 1894, pl. 1 figs. 1-6;—Geol. Mag., dec. 4, vol. 1, 1894, pl. 8;—Smithson. Misc. Coll., vol. 67, 1918, pl. 29, figs. 1-11; pl. 30, figs. 17-20; pl. 32; pl. 34, figs. 4-7; pl. 35, fig. 5.—Bernard, Quart. Jour. Geol. Soc., London, vol. 50, 1894, text figs. 11, 12.—Œhlert, Bull. Soc. Géol. France, ser. 3, vol. 24, 1896, text figs. 1-17, 34.—Jaekel, Zeits. d. d. geol. Gesell., vol. 53, 1901, text fig. 24. Moberg, Geol. Fören. Förhandl., vol. 29, pl. 5, 1907, pl. 4, fig. 2; pl. 5, fig. 1.—Handlirsch, Foss. Insekten, 1908, text fig. 6.—Tothill, Amer. Jour. Sci., vol. 42, 1916, p. 380, text fig. 5.—Crampton, Jour. N. Y. Entomol. Soc., vol. 24, 1917, pl. 2, fig. 20.
Historical.
Specimens of Triarthrus retaining appendages were first obtained by Mr. W. S. Valiant from the dark carbonaceous Utica shale near Rome, New York, in 1884, but no considerable amount of material was found until 1892. The first specimens were sent to Columbia University, and were described by Doctor W. D. Matthew (1893). This article was accompanied by a plate of sketches, showing for the first time the presence of antennules in trilobites and indicating something of the endopodites and exopodites of the appendages of the cephalon, thorax, and pygidium. Specimens had not yet been cleaned from the lower side, so that no great amount could then be learned of the detailed structure. Matthew concluded that "The homology with Limulus seems not to be as close in Triarthrus as in the forms studied by Mr. Walcott; but the characters seem to be of a more comprehensive type, approaching the general structure of the other Crustacea rather than any special form."
Professor Beecher's first paper, dated October 9, 1893, merely mentioned the fact that the Yale University Museum had obtained material from Valiant's locality, but was quickly followed by a paper read before the National Academy of Sciences on November 8, and published in December, 1893. This paper described particularly the thoracic appendages.
This was followed in January (1894 A) by an article in which some information about the mode of occurrence of the specimens was added, and in April (1894 B), the limbs of the pygidium were described and figured. The determination of the structure of the appendages of the head evidently presented some difficulty, for the article describing this portion of the animal did not appear until the next February (1895 A). This cleared up the ventral anatomy of Triarthrus, and was followed by a short article (1896 A) accompanied by a restoration of the trilobite showing all the appendages.
This ended Professor Beecher's publications on Triarthrus until his final paper in 1902, although he contributed some of his results and figures to his chapter on the trilobites in the Eastman-Zittel Text-book of Paleontology in 1900.
The discovery of these excellent specimens had of course excited very great interest. Doctor Walcott also studied a number of specimens from Valiant's locality, and published in 1894, with some original figures, the results of his comparison of the appendages of Triarthrus with those of Calymene and Ceraurus.
In his article on the "Systematic Position of the Trilobites," Bernard (1894) used the results of Professor Beecher's studies of 1893, and also quoted the papers by Matthew (1893) and Walcott (1894), though the article by the latter appeared too late to be used except for a note added while Bernard's paper was in press. A final footnote quoted from Professor Beecher's paper of April, 1894 (1894 B).
Œhlert (1896) gave an excellent summary in French of the work of Beecher and Walcott on Triarthrus, with reproductions of many of their figures.