THE ORDOVICIAN PERIOD 



101 



Fig. 58 

 Ordovician Trilobites: 1, la, Triarthrus becki (restorations by Beecher); 

 2, 2a, Bumastus trentonensis; j£ Acidaspis crosotus; 4, Trinucleus concen- 

 tricus; 5, Bronteus lunatus; 6, Ceraurus pleurexanthmus; 7, Isotelus maxi- 

 mus; 8,8a, Calymmene calicephala. (From Scott's " Introduction to Ge- 

 ology," permission of The Macmillan Company.) 



