1870.) Fr; ‘BILLINGS—LOWER-SILURIAN TRILOBITES, 483 
was first made known to science. It was named by Mr. Stokes. 
Very numerous figures of the doublure of different species of Trilo- 
bites 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 mem- 
branous 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 A. eapansus; and they were afterwards described and figured 
by Dr. A. Volborth in several papers*. He supposes them to indi- 
cate the points of attachment of soft swimming-feet. Hichwald 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. pla- 
tycephalus, 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 
pleure. 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 Tri- 
lobites ; and indeed they resemble, not remotely, those of our spe- 
cimen. 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.” J infer from this that the portion of the 
Transactions containing his paper was issued in 1825. De Kay’s paper, in which 
the species was first called /so¢elus gigas, was read before the New York Lyceum 
of Natural History, October 27th, 1825. Itis 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; (5) Mém. Acad. Imp. St. Pé- 
tersbourg, tome vi. No. 2, 1863; (4) Bull. Soc. Imp. Nat. Moscou, No, 1, 1866. 
I have only seen the last two of these. 
+ Lethea Rossica, vol. i. pt. 2. p. 1864, pl, 52. fig. 24, 
