The Appendages, Anatomy, and Relationships of Trilobites Part 5

8, fig. 9; Proc. Biol. Soc. Washington, vol. 9, 1894, pl. 1, fig.

9.

The specimen in the British Museum which Woodward called _Asaphus platycephalus_, is, in all probability, an _Isotelus gigas_. Woodward says of it:

I was at once attracted by a specimen of _Asaphus_, from the Black Trenton Limestone (Lower Silurian), which has been much eroded on its upper surface, leaving the hypostoma and what appear to be the appendages belonging to the first, second, and third somites, exposed to view, united along the median line by a longitudinal ridge. The pseudo-appendages, however, have no evidence of any articulations. But what appears to me to be of the highest importance, as a piece of additional information afforded by the Museum specimen, is the discovery of what I believe to be the _jointed palpus_ of one of the maxillae, which has left its impression upon the side of the hypostoma--just, in fact, in that position which it must have occupied in life, judging by other Crustaceans which are furnished with an hypostoma, as _Apus_, _Serolis_, etc.

The palpus is 9 lines in length, the basal joint measures 3 lines, and is 2 lines broad, and somewhat triangular in form.

There appear to be about 7 articulations in the palpus itself, above the basal joint, marked by swellings upon its tubular stem, which is 1 line in diameter.

[Ill.u.s.tration: Fig. 9.--A restored composite of _Isotelus maximus_ and _I. latus_. The exopodites are left out because entirely unknown.

Drawn by Doctor Elvira Wood. Natural size.]

Desiring to know more of this individual, I wrote to Doctor Bather and was surprised to learn that the specimen which was the basis of Woodward's observations is so badly preserved as to be of no real value. With his permission, I append a note made by Doctor Bather some years ago when selecting fossils to be placed on exhibition:

_Asaphus gigas_ Dekay. Ordovician, Trenton Limestone. N. America, Canada. Descr. H. Woodward, 1870, Q. J. G. S., XXVI, pp. 486-488, text fig. 1, as _Asaphus platycephalus_. Coll. and presd. J. J.

Bigsby, 1851. Regd. I 14431.

This specimen is in the Brit. Mus. Geol. Dept. I 14431. The supposed hypostome is exceedingly doubtful; it lies dorsad of the crushed glabellar skeleton. The "appendage" is merely the edge of a part in the head-shield; the maxilla is some calcite filling, between two such laminae.

13 Sept. 1911. (Signed) F. A. BATHER.

Walcott figured a slice of _Isotelus gigas_ from Trenton Falls, New York, which shows a few fragments of appendages, but is of particular importance because it shows the presence of well developed appendifers beneath the axial lobe.

=Isotelus arenicola= Raymond.

Ill.u.s.trated: Ottawa Nat, vol. 24, 1910, p. 129, pl. 2, fig. 5.

The following quotations from my paper are inserted here to complete the record of appendage-bearing specimens:

A rather remarkable specimen of this species was found by W. C.

King, Esq., on the sh.o.r.e of Lake Deschenes at Britannia [near Ottawa, Ontario]. This specimen is an impression of the lower surface of the trilobite, and shows a longitudinal ridge corresponding to the central furrow along the axis of the ventral side of the animal, ten pairs of transverse furrows, and the impression of the hypostoma. The doublure of the pygidium has also left a wide smooth impression, but in the cephalic region the hypostoma is the only portion of which there are any traces remaining. The specimen was found on a waterworn surface of the beach, partially covered by shingle....

The transverse furrows are the impressions left by the gnathobases of the basal joints of the legs. They were evidently long and very heavy, but the specimen has been so abraded that all details are obscured. The first six pairs of impressions are longer and deeper than the four behind. The first eight pairs seem to pertain to the thoracic appendages, while the last two belong to the pygidium.

From the posterior tips of the hypostoma to the first gnathobases of which traces are present there is a distance of about 22 mm.

without impressions. In _Isotelus gigas_ the hypostoma normally extends back to the posterior margin of the cephalon, so that it seems that in this specimen the impressions of the first two pairs of gnathobases under the thorax may not have been preserved. In that case, the six pairs of strong impressions may represent the last six pairs of thoracic segments, and the pygidium might begin with the first of the fainter ones.

_Horizon and locality:_ From the sandstone near the base of the Aylmer (Upper Chazy) formation at Britannia, west of Ottawa, Ontario.

Specimen in the Victoria Memorial Museum, Geological Survey of Canada, Ottawa.

The Appendages of Triarthrus.

=Triarthrus becki= Green.

(Pls. 1-5; pl. 6, figs. 1-3; text figs. 1, 10, 11, 33, 42.)

(Also see Part IV.)

Ill.u.s.trated: 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.--Oehlert, Bull. Soc. Geol. 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. Foren. Forhandl., 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 h.o.m.ology 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).

Oehlert (1896) gave an excellent summary in French of the work of Beecher and Walcott on _Triarthrus_, with reproductions of many of their figures.

Valiant (1901) in a non-technical article described his long search for trilobites with antennas. The discovery of the wonderful pyritized trilobites at Cleveland's Glen near Rome was not the result of a lucky accident, but the culmination of eight years of labor in a locality especially selected on account of the fineness of grain of the shale.

[Ill.u.s.tration: Fig. 10.--_Triarthrus becki_ Green. A new restoration, modified from Professor Beecher's, to incorporate the results of his later work. The inner ends of the endobases are probably too far apart, as it was not discovered until after the drawing had been made that the appendifers projected within the dorsal furrows. Drawn by Doctor Elvira Wood. about 3.8.]

After 1896, Professor Beecher turned his attention largely to the problem of the cla.s.sification of trilobites, and while he continued the arduous task of cleaning the matrix from specimens of _Triarthrus_ and _Cryptolithus_ he did not again publish upon the subject of appendages until forced to do so by the doubts cast by Jaekel (1901) upon the validity of his earlier conclusions. Because of certain structures which he thought he had interpreted correctly from a poorly preserved specimen of _Ptychoparia_, Jaekel came to the conclusion that Beecher's material was not well preserved. Professor Beecher would have taken much more kindly to aspersions upon his opinions than to any slight upon his beloved trilobites, and his article on the "Ventral Integument of Trilobites" of 1902 was designed not only as an answer to Jaekel, but also to show by means of photographs the unusually perfect state of preservation of the specimens of _Triarthrus_. This article, like so many describing the appendages of trilobites, beginning with Matthew's, was published in two places (Beecher 1902).

Most of Beecher's papers, except the last one, were reprinted in the volume ent.i.tled "Studies in Evolution," published by Charles Scribner's Sons at the time of the Yale Bicentennial in 1901. The part pertaining particularly to _Triarthrus_ is on pages 197 to 219.

Moberg (1907), in connection with a specimen of _Eurycare angustatum_ which he thought preserved some appendages, described and ill.u.s.trated some of the appendages of _Triarthrus_.

The most recent discussion of _Triarthrus_, with some new figures, is by Walcott (1918, p. 135, pls. 29, 30). He gives a summary of Beecher's work with numerous quotations. The princ.i.p.al original contribution is a discussion of the form and shape of the appendages before they were flattened out in the shale. He found also what he thought might possibly be the remains of epipodites on three specimens, one of which he ill.u.s.trated with a photograph. I have seen nothing which could be interpreted as such an organ in the many specimens I have studied.