TRTLOBITES. 



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 EntomoIUIms 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. t 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 souclie 

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

 mentioned Mollasca, and on the other, to the above-mcntioiied Crustacea, as well 

 as to Glomeris if, 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 exception 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. H They are named by some 

 authors Entomostracites. 



Hha ^Gwus AgnosfuSjBvow^!;., is tlie only one ^vhic]i lias the body either semicircular or kidncy-sliaped. In 

 all the other <;;enera it is oval or elliptic. 



Cali/mcne, lirong;., diil'ers from the others by the power it possessed of contracting: the body into a ball, in the 

 same manner as Sj)/ia;roma, Armadillo, Glomeris, that is, by causing the two extremities to approximate beneath 

 the breast. The shield, as broad or broader than lon^, exhibits, as in Asophtis and Ogygla, two eye-like eminences. 

 The segments do not extend laterally beyond the body, and are united to.i,^ether as far as the extremity; the body 

 is terminated posteriorly in a kind of triangular, elongated tail. 



• M. e' Deslongchanips, Professor at the Universiiy of Caen, the 

 Count de Rasoumouski, M. Dalman, and others, Imve recently pub- 

 lisliL-cI various observations upon llicsc fossils. M. V. Audouin, having 

 ailnincd the opininn ot Brongniart, huK opposed, id it memoir upon tliis 

 suhjeet, that whicli I h>id gisen. whereby I had appri>xini:iteil them to 

 tlic O;.cabriona. The most essential ditfieulty was to prove the ex- 

 istence of legs, and this he has tailed in doiiip. As to the ^.pplicatiou 

 of liis theory of the thor.-ix of inscLts to the Trilobites, it appears to 

 me tbc more douhtful. because, in my mode of looking at the subject, 

 llu' anterior segments of the abdomen of iusects alone represent the 

 thor'ix of tlic decapod Crustacea. 



■\ [Mr. [Parkinson] in his Outlines of Oryetoloi;ry, nevertheless be 

 lieves that he ha3 detected lliese organs, and that they are unijuicu- 

 Ir.leil. See also the EntomosCrticHe Grnuul-^iijr of Brongviart, Trilob., 

 iii. 0. [See also the 15th vol. of the Annaln des Sciences Naturvlles.'] 



J '1st edit, of tliis work, tom. iii. p. 150, 1.) No known Branchiopud 

 contracts itself into a ball. This character is eonfined, amon^'-st the 

 Crusiacca. lo Typhis, Sphreroma, Tytos, and Armadillo; and amongst 

 the apteruns in^iects, only to Glomeris, which is at the hend of its 

 eiass snd wjiich leaves a iprcat space between it ar.d the terminal 

 TTtistacca. Calymene evidently approaches, in respect lo the con- 

 t'r-iCtilUy, the last-mentioned insects. Typhis and Sphjcroma; but it 

 does uot'appear that the hind part of its body is provided with lateral 

 natatory iippendaj;es, a ncgatne cb:i 



which 



eparatcs them from 



Spli;eroma, but which approximates them lo 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 facetterl. In respect to their want 

 of superior anteiin;c. they have a further affinity with Limulus. 



§ It appears that in various Trilobites. and particularly in Asaphus, 

 the body is composed, in addition to tlie shield, of twelve segmi^nts 

 detached from eaeh other at the sides, and of another composint,' the 

 post-abdomen or tail, of a triang-ular or semilunar form, exhibiting 

 only superficial divisions, which do not cut the sides. In Pari-doxides, 

 on the contrary, its lateral lobes are terminated by acute prolonga- 

 tions, quite distiiict, and of vhich twenty-two are easily counted. A 

 species of Trilobite mentioned by Count Rasoumouski {.-inn. Sci. 

 A"*/;., June, 1S26, pi. xxviii. fig. 11), which he considers should form 

 a new (reiius, is very remarkable in this respect. Ita lateral lobes form 

 very long points. The feet of the pupa; of the gnats are In the forei 

 of lonij flattened plates, without articulations, terminated by filamcntH, 

 and folded back on the sides ; tliey are in a rudJmental state, and muy 

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

 is allied to the Paradoxitles. 



n 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. 



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