TRILOBITES. 449 



THE TRILOBITES. 



Near the Limuli and other Entomostraca provided •with, a great number of legs, 

 should be arranged, in the opinion of M. Alexandre Brongniart, and other natu- 

 ralists*, those singular fossil animals, at first confounded together under the common 

 denomination of Entomolithus paradoxus, but now called Trilobites, of which that 

 author has published an excellent monograph, illustrated by good lithographic figures. 

 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 

 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 

 primitive) of the articulated animals, being allied, on the one hand, to the last- 

 mentioned Mollusca, and on the other, to the above-mentiorxcd Crustacea, as well 

 as to Glomeris +, 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- 

 selves into a ball. Since the publication of the work of M. Brongniart, several natu- 

 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 

 appear to have been annihilated during the ancient revolutions of our planet. 



With the e.Kception of the heteromorphous genus, Agnostus, the Trilobites have, like 

 the Limuli, a large anterior segment, in the form of a shield, nearly semicircular, or 

 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. || They are named by some 

 authors Entomostracites . 



The g-enus Agnostus, Brons'., is the only one which has the body either semicircuhir or kidney-shaped. In 

 all the other genera it is oval or elliptic. 



Calymene, Brong., differs from the others by the power it possessed of contractine: the body into a ball, in the 

 same manner as SpJueroma, 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. 

 Tlie 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. Dcslonschamps, Professor at the University of Caen, the 

 Count de Rasoumouski, M. Dalinan, and others, have recently puh- 

 lished various observations upon these fossils. M. V. Audouin, having 

 adopted the opinion of Brongniart, has opposed, in a memoir upon tliis 

 suhject, that whicli I had g;iven, whereby \ had approximated them to 

 the Oscabrions. The most essential difficulty was to prove the ex- 

 istence of le;;s, 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 



Sphjeroma, 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 antennfc, they have a further affinity with Limulus. 



§ It appears that in various Trilobites, and particularly in .'\saphus, 

 the body is composed, in addition to the shield, of twelve segments 

 detached from each other at the sides, and of another composing the 



btful, because, in my mode of looking at the subject, i post-abdomen or tail, of a triangular or semilunar form, exhibiting 



segments of the abdomen of insects alone represent the 

 thorax of the decapod Crustacea. 



t Mr. [Parkinson] in his Outlines of Oryctology, nevertheless be 

 licves that he has detected these organs, and that tbey are unguicu- 

 lated. See also the Eniomostracite Granulenx of Brnn^uitirt, Trilub., 

 iii. 6. (See also the loth vol. of the Annnles det Science! Naturrlles.] 



i (Ist edit, of this work, tom. iii. p. I.i0, 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- 

 tractilitv, the last-mentioned insects, Typhis and Sphaeroma; but it 

 does not appear that the hind part of its body is provided with lateral 



only superficial divisions, which do not cut the sides. In Par:.doxides, 

 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 (./wn. Sci. 

 Nat., June, 1826, pi. xxviii. fig. 11), which he considers should form 

 a new genus, is ven,- remarkable in this respect. Its lateral lobes form 

 very long points. The feet of the pupae of the gnats are in the form 

 of long flattened plates, without articulations, terminated by filaments, 

 and folded back on tlie sides ; they are in a rudimental state, and may 

 be analogous to the lateral divisiocs of this species of Trilobite which 

 is allied to the Paradoxides. 



B The Squillffi, 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 



Bt.uory appendages, a negative character, which separates them from ' not form deep chainiels. 



(i G 



