INTRODUCTION. 7 



of Trilobites as T. coniir/crun, directing attention, according to Bcckmann's and Briinicli's 

 example, to the necessity of distinguishing several species of these animals. This very correct 

 view he furtlier carried out in his ' Pctrefaktenkunde' of 1820, in which he speaks of five 

 different species, two of which, however, belong to doubtful forms. All the three authors 

 are of opinion that the Trilobites are Crustacea, without, however, determining their more 

 intimate affinity with any particular group. 



SECTION V. 



The year 1821 is a crisis in the literary history of the Trilobites, for a new epoch then 

 commences, which may be designated as the period of the more accurate study of them. 

 Four distinguished observers, Latreille, Audouin, Wahlenberg, and Brongniart, published the 

 result of their studies in or immediately after this period, the two former only paying regard 

 to the organization of these animals, the two latter describing the differences of the species. 



P. A. Latreille, the best authority on the subject of the Articulata, both with respect to 

 the general subject and its details, might certainly claim attention to his opinion on the affinity 

 of the Trilobites ; but he performed his task in a manner which could by no means satisfy those 

 acquainted with the subject. After having formerly determined in favour of the affinity of 

 the Trilobites to the Articulata (Cuv. Regne Anim., prem. ed. torn, iii), he here contradicts 

 this opinion altogether, and endeavours to prove, by the absence of feet, that the Trilobites 

 must be most nearly related to Chiton. He not only, therefore, overlooked the articulation of 

 the body, pervading all parts of it, but also the eyes ; he asserts also, that if feet had been 

 existing they must be recognizable, and from their absence draws the conclusion that the 

 Trilobites are Mollusca. 



V. Audouin, who probably had only shortly before completed his work on the skeleton 

 of the Articulata (Annal. des Scienc. Natur., pr. ed. tom. i, 1824), had also been led by these 

 studies to the subject of the Trilobites, and soon recognized their articulate nature from the 

 remains of the crust. But he evidently went too far in transferring the results he had so readily 

 arrived at with regard to insects to the other groups of the Articulata, and in this he sought 

 analogies which do not exist in reality. Indeed, even his own investigations with regard to 

 the abdomen of the Macrura, with which, as with the thorax of the IsopoJa, he very justly 

 compares the crust of the Trilobites, ought to have convinced him that the cpisterna and ejjimera, 

 two portions of the thorax of insects which are separated by particular sutures, do not at 

 all exist in the gi'oups enumerated, and that even the boundary between back and sternum is 

 an artificial one. He nevertheless views the lateral lobes of the shell, which in many of the 

 Trilobites are separated by an oblique diagonal furrow into an anterior and posterior half, as 

 analogues of those parts, terming the anterior cpisternum, the posterior epimerum, and the 

 middle part of each tergum; appellations manifestly unsuitable, since several Trilobites 

 (e. g. Illanus) do not possess this separating furrow at all, and in no single species of them do 

 the regions distinguished by him constitute isolated pieces connected by sutures. AVe arrive, 

 however, in spite of these subtleties, for which there is no natural foundation, at the four 

 following facts, namely, — 



1st. That Trilobites differ only from the other Articulata in points of secondary 

 importance, and that, beyond a doubt, they belong to this group of the animal kingdom. 



