556 



GEOLOGY 



withdrawal of the epicontinental waters from the larger part of 

 the interior, and to the conversion of the remainder into an excess- 

 ively salt sea, in the deposits of which few fossils are found. The 

 Waterlime beds represent a gradual return in the Salina basin of 

 conditions hospitable to life. The fauna of these beds is limited, 

 but radically unlike that of the Niagaran epoch. Most of the 



Fig. 406. Crustaceans other than Trilobites (a, b and c),and Fish (d): a, Eu- 

 rypterus fischeri Eich., restoration after Schmidt; b, Pterogotus anylicits 

 Agass., restoration after Woodward; c, Palceophonus c(ilc<l<iicns 

 Hunter, after Peach; d, Palceaspis americana Claypole, restoration by 

 Claypole, modified by Dean. 



familiar marine types are absent from the later fauna, and its signal 

 feature was an abundance of large crustaceans of types barely 

 represented before. The most characteristic of these were the 

 great Eurypterus (Fig 406, a) and the still more gigantic Pfrrinjotnx 

 (b). The former reached a length of a foot and a half or more, and 

 the latter attained a length of over six feet in the next period. 

 These were gigantic dimensions for crustaceans, and were probably 

 never surpassed. These giants among their kind seem clearly to 



