§21. 



SILURIAN TRILOBITES. 



789 



These remarkable crustaceans, which constituted the 

 great mass of the population of the paleozoic seas, have the 

 body protected by a strong dorsal case or shell composed 

 of numerous annular segments, or arches, and which is 

 generally divided into three lobes by two longitudinal 

 furrows or depressions. The head and abdomen are each 

 covered by a single piece. The eyes of most of the genera 

 are very large and reticulated, consisting of numerous dis- 

 tinct facets or lenses, as in other crustaceans, and are 

 implanted on the cephalic buckler. No traces of pats, feet, 

 or swimmers, have been detected, and it is therefore sup- 



Lign. 178. — Trilobite ih Silurian limestone; from Dudley. 

 {Calymene* Blumenbachii.) 



posed that these appendages were composed of a soft and 

 perishable substance.f 



* Calymene, signifying concealed : in allusion to the non-discovery 

 of legs or antennae. 



| Consult Medals of Creation, pp. 552-556. 

 3 f 2 



