was first made known to science. It was named by Mr. Stokes. Very numerous figures of the doublure of different species of Trilobites may be seen in the large works of Barrande, Salter, and others ; but it is described by some as a portion of the crust, folded under to give greater strength to the margins of the head and tail. This, however, is not the whole of its interpretation. It is (as above stated) a part of the underside, which, on account of its greater thickness and hardness, is usually preserved, while the more membranous and fragile portions have disappeared.
About twelve years ago, Dr. Pander discovered some small scars and tubercles on the inner surface of the doublure of the Russian Trilobite-4. expansus; and they were afterwards described and figured by Dr. A. Volborth in several papers*. He supposes them to indicate the points of attachment of soft swimming-feet. Eichwald has also described and figured the same organs in A. Schlotheimii, but maintains that they are the sockets of the first segments of hard, horny, articulated, ambulatory legs†. These two distinguished naturalists have discussed the points in difference between them at length, and with their well-known ability, in the works cited below. I have discovered the same organs in three of our species — A. platycephalus, A. canadensis, and A. megistos. They are small rounded or ovate scars, with an elevated protuberance on one side. They are situated on the doublure, close to the anterior margins of the pleurae. The protuberance leaves a small but distinctly marked pit in the cast of the interior, as is shown in Pl. XXXI. fig. 5. That organs of some kind were here attached, I think there can be little doubt. But what was their function? If they were legs, then Asaphus must have had four parallel rows of limbs beneath the thorax. If the two inner rows were ambulatory, as I suppose those of our Trilobite to have been, then the two outer rows may have been natatory, as Dr. Volborth maintains. Eichwald figures several slender articulated organs, which he supposes to be the legs of Trilobites ; and indeed they resemble, not remotely, those of our specimen. For convenience of reference, I have copied his figures (Plate XXXI. fig. 6). If they are truly the same organs, he would still be, to some extent, wrong ; for he thinks they were attached to the doublure.
read February 21st, March 7th, and 21st, 1823. It is usually cited under the date of 1822. In his article on the Minerals and Fossils of Canada, published in Silliman's Journal in 1824, vol. viii. p. 84, he alludes to it thus: — "I beg to refer to three figures of large unknown trilobites, published last year in the Geological Transactions of London." I infer from this that the portion of the Transactions containing his paper was issued in 1823. De Kay's paper, in which the species was first called Isotelus gigas, was read before the New York Lyceum of Natural History, October 27th, 1823. It is generally quoted with the date 1824.
- (1) Deutsche Petersb. Akad. Zeitung, 1857, No. 255 ; (2) Verhandl. der
kaiserl. miner. Gesellsch. Jahrg. 1857-58, p. 168; (3) Mem. Acad. Imp. St. Petersbourg, tome vi. No. 2, 1863; (4) Bull. Soc. Imp. Nat. Moscou, No. 1, 1866. I have only seen the last two of these.
†Lethaea Rossica, vol. i. pt. 2. p. 1364, pl. 52. fig. 24.
