Handbook of Paleontology 231 



all over the world. The trilobites were its most char- 

 acteristic animals. Nearly all the brachiopod shells 

 were horny „,and the limpetlike shells commonly classi- 

 fied as gastropods. The corallike animals were almost 

 restricted to this epoch. The life of the Middle and 

 Upper Cambrian showed greater variety but, as in the 

 Lower Cambrian, was chiefly trilobites and brachio- 

 pods. The faunas were no longer cosmopolitan but 

 with the Middle Cambrian two realms or provinces are 

 recognized, that of the North Atlantic or Acadian and 

 that of the Pacific or Albertan, both of which have been 

 discussed above. Both trilobites and brachiopods of 

 the Middle Cambrian of the Cordilleran area were more 

 numerous than in the Lower Cambrian, the trilobites 

 constituting about half the faunas. Trilobites showed 

 greater variety and among the genera found were 

 Bathyuriscus, the most prevalent form, Olenoides, Neo- 

 lenus, Ogygopsis etc. The Burgess shale in the Cana- 

 dian Rockies, near Field, British Columbia, has yielded 

 a collection of organisms including worms, sea cucum- 

 bers, jellyfishes, and a most interesting array of crusta- 

 ceans (branchiopods, phyllocarids, primitive and spe- 

 cialized trilobites etc.). The Acadian or Middle Cam- 

 brian fauna of the Atlantic Area, known as the Paro- 

 doxides fauna, because characterized by that trilobite 

 genus, has a distinctly different character, showing a 

 similarity to the fauna of western Europe which also 

 belongs to the Atlantic realm. The Upper Cambrian 

 (St. Croixian) epoch has also its characteristic trilobites, 

 among them Dicellocephalus, Illaenurus and Crepi- 

 cephalus. Eurypterids occur here for the first time. 

 Brachiopod genera with calcareous shells are more 

 frequent and coiled gastropods have appeared. 



