Observations on Trilobites. 175 



Post-abdomen or tail, broad, expanded with indistinct divi- 

 sions, as large as the buckler. 

 Longitudinal lobes very distinct. 



This genus will be sufficiently distinguished from the five 

 genera, proposed by M. Alexandre Brongniart, in his valua- 

 ble and truly philosophical work on the Trilobites, by the fol- 

 lowing particulars. 



From Calymene. By the presence of but two tubercles on 

 the buckler, not reticulated ; by the abdomen with but eight 

 articulations. 



From Asaphus. By the middle lobe which is double the size 

 of the lateral ones ; by the absence of a membranous expan- 

 sion on the sides ; by the non-reticulation of the eyes, &c. 



From Ogygia. By the rolled form ; the rounded posterior 

 angles of the buckler, and the distinct articulation of the lon- 

 gitudinal lobes. 



From Paradoocide and Agnoste, by characters too obvious 

 to be enumerated.* 



* Note. As the work of M. Brongniart is expensive and rare, and has 

 never been translated, we have annexed an abstract of his genera cf 

 Trilobites. 

 Genus Calymeine. 



Body contracted into nearly a semi-cylindrical sphere. 



Buckler with many tubercles or folds. Two reticulated eye-shaped 



tubercles. 

 Abdomen and post abdomen with entire edges ; abdomen divided int* 

 twelve or fourteen articulations. 

 No elongated tail. 



4 species. 

 Senus Asaphus. 



Body broad and rather flat ; middle lobe prominent and very distinct. 

 Flanks or lateral lobes, each double the size of the middle lobe. 

 Submembranous expansions extending beyond the lateral lobes. 

 Buckler semicircular, furnished with two reticulated eye-shaperi 



tubercles. 

 Abdomen divided into 8 or 12 articulations. 



5 species. 



