CAMBRIAN INVERTEBRATES 



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first known in the Silurian, and through it arose the entire 

 group of arachnoid (spider-hke) animals, including the existing 

 •scorpions, spiders, and mites. It is also possible that the 



Fig. 31. EuRYPTERiDS OR Sea-Scorpions of Silurian Times. 



A. Restoration of the giant eurypterid, Stylonurus excelsior, from the Catskill sandstone. 



Natural length, four feet. 



B. Restoration of Eusar.cus, from the Bertie water-lime. Natural length, three feet. 



C. Restoration of Eiisarcus, age of the Bertie water-lime. (After John M. Clarke.) 



amphibious, terrestrial, and aerial Insecta were derived from 

 some Silurian or Devonian chitin-armored articulate. The 

 true Crustacea also have probably developed out of the same 



