Observations on Trilobites. 179 



arranged with it, as some of its characters would seem to 

 vender it inadmissible into the genus Asaphus, unless its 

 present characters should be modified or altered. It is im- 

 possible, however, to speak positively without an examination 

 of the specimen itself. 



Of the nature of Trilobites. 



Various conjectures have been hazarded respecting the 

 nature of these extinct animals, and its affinities with recen 1 

 species. It has been described as a shell with three lobes' 

 as the larva of an insect, as a perfect insect, as analogous to 

 the genera Chiton and Patella of shells, and more recently to 

 the class of crustaceous animals. 



M. Latreille, in a paper entitled, " Affinites des Trilobites" 

 published 1821, maintains that they bear the nearest affinity 

 to the genus Chiton. He supposes their articulated bodies, 

 the membranous border evident in some of them, and their 

 supposed habitations, to corroborate this opinion. On the other 

 hand, he asserts that the absence of antenna? and of feet, are 

 fatal objections to their being classed with crustaceous animals. 

 He also alludes to the fact of Trilobites having prominent 

 eyes ; and according to him, those Crustacea which have been 

 considered most analogous to Trilobites, are not furnished 

 with equally prominent organs of vision. 



M. Alexandre Brongniart, on the other hand, argues that 

 Trilobites are crustaceous animals, from the following consid- 

 erations. The general form of Trilobites ; their constant 

 division into a head which is confounded with the buckler, an 

 abdomen, and a post-abdomen or tail ; the sessile position 

 of the eyes ; the rough and tubercular teguments ; the great 

 number of transversal articulations, and finally, even the man- 

 ner of contracting itself into a ball, present an assemblage of 

 characters which belong only to the Crustacea of the order 

 Gymnobranchia. The trilobate division of these animals, led 



