TRILOBITES. 
449 
THE TRILOBITES. 
ij Near the Limuli and other Entomostraca provided with a great number of legs, 
;j should be arranged, in the opinion of M. Alexandre Brongniart, and other natu- 
I ralists*, those singular fossil animals, at first confounded together under the common 
|| denomination of Entomolitims paradoxus, but now called Trilobites, of which that 
;! author has published an excellent monograph, illustrated by good lithographic figures. 
I According to this hypothesis, we must admit, as a positive fact, or at least as most 
probable, the existence of locomotive organs, although, notwithstanding all research, 
' no vestige of them has yet been detected. f Supposing, on the other hand, these fossil 
I animals to be destitute of such organs, I have supposed that they are more naturally 
; allied to the Oscabrions, or rather that they formed the primitive type (la souche 
j primitive) of the articulated animals, being allied, on the one hand, to the last- 
; mentioned Mollusca, and on the other, to the above-mentioned Crustacea, as well 
I as to Glomeris f, to which certain Trilobites, such as Calymene, make an approach 
; as well as to the Oscabrions, because, like them, they are capable of contracting them- 
I selves into a ball. Since the publication of the work of M. Brongniart, several natu- 
I ralists have not agreed with his opinion, but, on the other hand, have either partially 
! or entirely adopted mine : others still hesitate. Be this as it may, these animals 
I appear to have been annihilated during the ancient revolutions of our planet. 
; With the exception of the heteromorphous genus, Agnostus, the Trilobites have, like 
j the Limuli, a large anterior segment, in the form of a shield, nearly semicircular, or 
I lunulated, and succeeded by about twelve to twenty-two segments §, all, except 
the last, being transverse, and divided by two longitudinal furrows into three rows of 
lobes, whence the origin of the name of Trilobites. jj They are named by some 
! authors Entomostracites. 
The genus Agnostus, Brong., is the only one which has the body either semicircular or kidney-shaped. In 
all the other genera it is oval or elliptic. 
Calymene, Brong., ditfers from the others by the power it possessed of contracting the body into a ball, in the 
same manner as Spharoma, Armadillo, Glomeris, that is, by causing the two extremities to approximate beneath 
the breast. The shield, as broad or broader than long, exhibits, as in Asaphus and Ogygia, two eye-like eminences. 
The segments do not extend laterally beyond the body, and are united together as far as the extremity ; the body 
is terminated posteriorly in a kind of triangular, elongated tail. 
* M. E. Deslongchamps, Professor at the University of Caen, the 
Count de Rasoumouski, M. Dalraan, and others, have recently pub- 
lished various observations upon these fossils. M. V. Audouin, having 
adopted the opinion of Brongniart, has opposed, in a memoir upon this 
subject, that which I had given, whereby I had approximated them to 
the Oscabrions. The most essential difficulty was to prove the ex- 
istence of legs, and this he has failed in doing. As to the application 
of his theory of the thorax of insects to the Trilobites.it appears to 
me the more doubtful, because, in my mode of looking at the subject, 
the anterior segments of the abdomen of insects alone represent the 
thorax of the decapod Crustacea. 
t Mr. [Parkinson] in his Outlines of Oryctology, nevertheless be 
lieves that he has detected these organs, and that they are unguicu- 
lated. See also the Entomostracite Granuleux of Brongniart, Trilob., 
iii. 6. [See also the loth vol. of the Annales des Sciences Naturelles.] 
t (1st edit, of this work, tom. iii. p. 150, 1.) No known Branchiopod 
contracts itself into a ball. This character is confined, amongst the 
Crustacea, to Typhis, Sphaeroma, Tylos, and Armadillo ; and amongst 
the apterous insects, only to Glomeris, which is at the head of its 
class, and which leaves a great space between it and the terminal 
Crustacea. Calymene evidently approaches, in respect to the con- 
tractility, the last-mentioned insects, Typhis and Sphajroma ; but it 
does not appear that the hind part of its body is provided with lateral 
natatory appendages, a negative character, which separates them from 
Sphaeroma, but which approximates them to Armadillo, and especially 
to Tylos. The examination of a specimen well preserved has convinced 
me that they had, like the Limuli, dorsal eyes, with two elevations, of 
which the cornea was granulose or facetted. In respect to their want 
of superior antennae, they have a further affinity with Limulus. 
§ It appears that in various Trilobites, and particularly in Asaphus, 
the body is composed, in addition to the shield, of twelve segments 
detached from each other at the sides, and of another composing the 
post-abdomen or tail, of a triangular or semilunar form, e.xhibiting 
only superficial divisions, which do not cut the sides. In Paradoxides, 
on the contrary, its lateral lobes are terminated by acute prolonga- 
tions, quite distinct, and of which twenty-two are easily counted. A 
species of Trilobite mentioned by Count Rasoumouski (Ann. Sci. 
Nat., June, 1826, pi. x.xviii. fig. 11), which he considers should form 
a new' genus, is very remarkable in this respect. Its lateral lobes form 
very long points. The feet of the puprn of the gnats are in the form 
of long flattened plates, without articulations, terminated by filaments, 
and folded back on the sides ; they are in a rudimental state, and may 
be analogous to the lateral divisions of this species of Trilobite which 
is allied to the Paradoxides. 
I The Squilla;, various Amphipod and Isopod Crustacea, have also 
many of their segments divided into three portions by two impressed, 
longitudinal lines, but these lines are nearer to the margin, and do 
not form deep channels. 
G G 
