P^CILOPODA. 
273 
that these animals were deprived of them, I thought tliat their natural 
position was in the neighbourhood of the Chitones, or rather that 
they constituted the original stock of the Articulata, being con- 
nected on the one hand with these latter Mollusca, and on the other 
with those first mentioned, and even with the Glomeres *, to which 
some Trilobites, such as the Calymenes, appear to approximate, as 
well as to the Chitones, inasmuch as by contracting they could also 
become spherical. Since the publication of M. Brongniart’s work, 
some naturalists have rejected his opinions and adopted mine, either 
wholly or in part ; others still hesitate. Be this as it may, these 
animals appear to have been annihilated by some ancient revolution 
of our planet. 
The Trilobites, one heteromorphous genus excepted, that of 
Agnostus, have, like the Liinuli, a large anterior segment in the form 
of an almost semicircular or lunated shield, followed by from about 
twelve to twenty-two segments |, all transversal except the last, and 
divided by two longitudinal sulci into three ranges of parts or lobes, 
whence their name of Trilobites Some naturalists call them 
Entomostracites. 
* First edition of the R^gne Animal, tome III, p. 150, 151. There is no Bran- 
chiopoda known which can contract itself into the form of a ball. This character is 
peculiar to Typhis, Sphaeroma, Tylos, and Armadillo among the Crustacea, and, 
among the class of apterous Insects, to Glomeris, a genus which is at the head of that 
class, and which leaves between it and the latter Crustacea a considerable hiatus. 
The Calymenes, with respect to this contractility, evidently approach these latter 
Insects, the Typhes and Sphseromte ; but it does not appear that the posterior 
extremity of their body is provided with lateral natatory appendages, a negative cha- 
racter, which would remove them from the Sphaeromae, but approximate them to 
Armadillo, and particularly to Tylos, where the superior part of the thoracic segments 
is divided into three. The study of a well-preserved specimen has convinced me that, 
like the Limuli, they had eyes placed against two prominences, and that the cornea 
was granulous or with facets. The non-existence of the superior antennae also 
indicates a new affinity between these same Trilobites and the Limuli. 
-h The body of various Trilobites, and particularly of the Asaphi, seems to consist, 
exclusive of the shield, of twelve segments, well separated on the sides, and of 
another forming the post-abdomen, or a triangular or semi-lunar tail, whose divisions 
are superficial and do not cut its edges. In the Paradoxides, on the contrary, the 
lateral lobes terminate by well marked acute prolongations, and twenty-two of them 
can be distinctly counted. A species of Trilobite, mentioned by Count Rasoumowski 
in his memoir on fossils, Ann. des Sc. Nat. June, 1826, pi. xxviii, ii, which he pre- 
sumes should constitute a new genus, is, in ' this respect, very remarkable. Its 
lateral lobes form very long thongs or slips tapering to a point. The feet of the 
pupae of the Culices are elongated, flattened, inarticulated laminae terminated by 
threads and folded on the sides. They are in a rudimental state, and may be 
analogous to the lateral divisions of this species of Trilobite, allied to the Para- 
doxides. 
I The Squillse, and various Ampbipodous and Isopodous Crustacea have .also 
several of their segments trisected by two impressed and longitudinal lines ; but 
these lines are nearer to the edges and do not form dppn sulci. 
VOL. III. 
T 
