ORDER TR1L0BITES. 
379 
them seems to have been discovered. M. Outlines, indeed, 
in his Oryctology, thinks that he has perceived something ol 
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 primitive 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 calymense, 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, 
