TklLOBITES AND OTJIER FOSSIL CktJSTACEA. itg 



geological systems. Thus, Paradoxides and Agnostus 

 are peculiarly Cambrian ; Trmiicleus and Asaphtis 

 are almost exclusively Lower Silurian ; Phacops and 

 Calyinene are markedly Upper Silurian ; Brontes and 

 Harpes are among characteristic Devonian fossils ; 

 whilst Phillipsia and Griffithsides are genera of small 



Fig. 152, — Paradoxides Davidis. 



Fig. i53.—//oma/anoius, 



Trilobites— the last of their race — which are peculiar 

 to the Carboniferous limestones. 



Undoubtedly many of the fossil Tribolites we 

 meet with in any of the above rocks are inotdts — that 

 is, portions of the carapace thrown off after the 

 manner of the shells of lobsters and crabs. This 



