JMSCILOPODA. 273 



that these animals were -deprived of them, I thought that their natural 

 position was in the neighbourhood of the Chitones, or rather that 

 they constituted the original stock of the Articulata, being con- 

 n<rted on the one hand with these latter Mollusca, and on the other 

 with those first mentioned, and even with the Glomeres *, to which 

 some Trilobites, such as the Calymenes, appear to approximate, as 

 well as to the Chitones, inasmuch as by contracting they could also 

 !) -come spherical. Since the publication of M. Brongniart's work, 

 some naturalists have rejected his opinions and adopted mine, either 

 wholly or in part ; others still hesitate. Be this as it may, these 

 animals appear to have been annihilated by some ancient revolution 

 of our planet. 



The Trilobites, one heteromorphous genus excepted, that of 

 Agnostus, have, like the Limuli, a large anterior segment in the form 

 of an almost semicircular or lunated shield, followed by from about 

 twelve to twenty-two segments f, all transversal except the last, and 

 divided by two longitudinal sulci into three ranges of parts or lobes, 

 whence their name of Trilobites J. Some naturalists call them 

 Entomostracites. 



* First edition of the Kegne Animal, tome III, p. 150, 151. There is no Bran- 

 chiopoda known which can contract itself into the form of a ball. This character is 

 peculiar to Typhis, Sphaeroma, Tylos, and Armadillo among the Crustacea, and, 

 among the class of apterous Insects, to Glomeris, a genus which is at the head of that 

 class, and which leaves between it and the latter Crustacea a considerable hiatus. 

 The Calymenes, with respect to this contractility, evidently approach these latter 

 Insects, the Typhes and Sphaeromae ; but it does not appear that the posterior 

 extremity of their body is provided with lateral natatory appendages, a negative cha- 

 racter, which would remove them from the Sphaeromae, but approximate them to 

 Armadillo, and particularly to Tylos, where the superior part of the thoracic segments 

 is divided into three. The study of a well-preserved specimen has convinced me that, 

 like the Limuli, they had eyes placed against two prominences, and that the cornea 

 was granulous or with facets. The non-existence of the superior antennae also 

 indicates a new affinity between these same Trilobites and the Limuli. 



f The body of various Trilobites, and particularly of the Asaphi, seems to consist, 

 exclusive of the shield, of twelve segments, well separated on the sides, and of 

 another forming the post-abdomen, or a triangular or semi-lunar tail, whose divisions 

 are superficial and do not cut its edges. In the Paradoxides, on the contrary, the 

 lateral lobes terminate by well marked acute prolongations, and twenty-two of them 

 can be distinctly rountrd. A s pi-pies of Trilobitr, mentioned by Count Rasoumowski 

 in his memoir on fossils, Ann. des'Sc. Nat. June, 1826, pi. xxviii, ii, which he pre- 

 sumes should constitute a new genus, is, in this respect, very remarkable. Its 

 lateral lobes form very long thongs or slips tapering to a point. The feet of the 

 pupoe of the Culices are elongated, flattened, iuarticulated laminae terminated by 

 threads and folded on the sides. They are in a rudimental state, and may be 

 analogous to the lateral divisions of this species of Trilobite, allied to the Para- 

 doxidet. 



J The Squillac, and various Amphipodous and Isopodous Crustacea have also 

 several of their segments trisected by two impressed and longitudinal lines ; but 

 these lines are nearer to the edges and do not form d*en sulri. 



VOL. HI. T 



