ORDER TRILOBITES. 379 



them seems to have been discovered. M. Outlines, indeed, 

 in his Oryctology, thinks that he has perceived something of 

 this kind, and that they are unguiculated. M. Victor 

 Audouin, embracing with ardour the opinion of M. Brogniart, 

 has combated in a particular memoir, the one which I put 

 forth on this subject, and according to which, I approximated 

 them to chiton. The most essential part of the difficulty was 

 to authenticate the existence of the feet, which he has not 

 done. As for the application of his theory of the thorax of 

 insects to the trilobites, it appears to me so much the more 

 doubtful, as, according to my views, the first rings of the ab- 

 domen of the insects, alone represent the thorax of the decapod 

 Crustacea. 



Supposing, on the contrary, those animals to be deprived 

 of feet, they come more naturally near the chitones, or rather, 

 perhaps, they formed the piimitive source of the articulated 

 animals, being connected on the one side with these last 

 mollusca, and on the other with the above mentioned Crus- 

 tacea, and even with glomeris, to which some trilobites, such 

 as the calymenae, appear to approximate, as well as to Chiton, 

 inasmuch as they could also assume in contracting, the form 

 of a spheroid. Since the publication of the work of M. 

 Brogniart, some naturalists have not agreed with him in 

 opinion, and have wholly or in part, adopted mine ; others 

 still hesitate. Be this, however, as it may, these animals 

 appear to have been annihilated by the ancient revolutions 

 of our planet. 



If we except an heteromorphous genus, that of Agnostus, 

 the trilobites have, as well as the limuli, a large anterior seg- 

 ment, in the form of a shield, almost semi-circular, or lunu- 

 lated, and followed by about from twelve to twenty- two seg- 

 ments, all, with the exception of the last, transverse, and 

 divided by two longitudinal furrows, into three ranges of parts. 



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