ORDER TRILOBTTES. 381 



broad, or broader, than long, presents, as in Asaphus and 

 Ogygia, two oculiform eminences. The segments do not 

 edge out beyond the body laterally, they are united as far as 

 the end, and the body is terminated posteriorly in a sort of 

 triangular and elongated tail. 



In Asaphus, Brogn., the oculiform tubercles appear to 

 present a lid, or are granular. The sort of tail which ter- 

 minates the body posteriorly, is less elongated than in caly- 

 mene, and either almost semi-circular, or in the form of a 

 short triangle. In the asaphus of Brogniart, described and 

 figured by M. Eudes des Longchamps, the posterior angles 

 of the buckler, instead of being directed backwards, as in the 

 other species, are recurved. 



The buckler of Ogygia, Brogn., is longer than broad, 

 with the posterior angles elongated like a spine. The oculi- 

 form eminences present neither lid nor granulation. The 

 body is elliptical. 



These eminences having the appearance of eyes, do not 

 exist, or do not at all appear in the genus Paradoxides, 

 Brogn. The segments, or at least most of them, out-edge the 

 body laterally, and are free at their lateral extremity. 



Such are the characters of the five genera established by 

 M. Alexandre Brogniart, and which may be distributed into 

 three principal groups; the reniformes, (genus Agnostus) 

 the contractiles (genus Calymene) and the ext ensiles, 

 (genera AsAPHUs, Ogygia, and Paradoxides). 



We shall refer, for the knowledge of the species and their 

 localities, to the admirable labours of this naturalist, who, 

 with respect to the fossil Crustacea, properly so called, or 

 clearly recognized to be such, has associated with himself 

 one of his first pupils, and a correspondent of the Academy of 

 Sciences, M. Anselm Gaetan Desmarest, often cited by us, 

 both for this part, and his work on the living Crustacea. 



