17 



Genus Fifth. AGNOSTUS. 



Body ellipsoidal semicylindrical. 



Buckler and flanks edged the edges being slightly 

 elevated. 



Middle lobe with two transverse divisions, each com- 

 posed of a single piece. 



Two glandular tubercles on the anterior part of the 

 body. 



In 1824, Dr. J. E. Bekay added a sixth genus to 

 the family of the trilobites, which he describes in the 

 following manner. 



Genus Sixth. ISOTELUS, 



Body oval oblong, often contracted, not unfrequent- 

 ly extended. 



Head or buckler large and rounded, equalling the 

 tail in size, with but two oculiform tubercles. 



Abdomen with 8 articulations. 



Frontal process beneath, with two semilunar ter- 

 minations. 



Post-abdomen or tail broad, expanded with indis- 

 tinct divisions, as large as the buckler. 



Longitudinal lobes very distinct. 



This genus, he remarks, will be sufficiently distin- 

 guished from the five genera proposed by M. Jllexan- 

 dre Brongniart in his valuable and truly philoso- 

 phical work on the trilobites by the following parti- 

 culars. 



From Calymene. By the presence of but two tu- 

 B 2 



