TRILOBITES, dze. 



GENUS CALYMENE. Brongniart. 



THE name of this genus is derived from a Greek 

 word which signifies obscure or concealed. The fossil 

 animals included by it are characterized as having 

 contractile bodies; the buckler as bearing many tu- 

 bercles or folds the cheeks as being oculiferous, 

 and the abdomen and tail as being composed of from 

 twelve to fourteen articulations or joints, without 

 any membranaceous expansion. The Calymenes in 

 thickness are nearly semicylindrical, and the buck- 

 ler in front presents a chaperon or upper lip more or 

 Jess raised. In perfect specimens, there is a small 

 furrow which seems to indicate a separation between 

 the upper and under parts of this kind of lip. The 

 eyes are always raised, and frequently present the re- 

 markable structure observable in many of the Crusta- 

 cea; but as this part is generally very prominent, the 

 reticulations of the eye are commonly worn off or in- 

 jured. 



Professor Brongniart places but little confidence 

 in any of the generic characters above enumerated, 

 except the number of articulations of the abdomen: 



