THE ORDOVICIAN PERIOD 



533 



Fishes. Fragmentary fossils of fishes constitute the most strik- 

 ing innovation in the record of the marine life of the Ordovician 

 periocT These have been found in a few localities only, notably 

 near Canyon City, Colo., and in the Bighorn Mountains of Wyoming. 



Fig. 395. Ordovician Sponges: a, Receptaculites occidentalis Salter; 6, 

 Brachiospongia digitata Beecher; c, Archceocyathus minganensis Billings; 

 d, Strotospongia maculosa U. and E.; e, Ischadites, species undetermined. 

 The Receptaculites and Ischadites have sometimes been regarded as giant 

 foraminifers. 



Implied life. If we inquire what forms other than those fossil- 

 ized are necessary to round out a rational assemblage of life, a 

 briefer answer may be given than in the case of the Cambrian life, 



Fig. 396. Ordovician Annelids: a, Ardbellites cornutus Hinde; b, Glycerites 



sulcatus Hinde; c, Eunicites gradlis Hinde; d, Arabellites ovalis Hinde; 



. e, Eunicites varians (Grinnell); /, Oenonites rostratus Hinde; g, Ortonia 



minor. Nicholson, a-e are highly magnified illustrations of the jaws of 



annelids. 



for the Ordovician fauna was a nearer approach to a theoretically 

 complete assemblage. As in the Cambrian, a vast supply of un- 

 recorded vegetation must be postulated as a food-supply. To 

 provide for organisms that preyed upon one another in succession, 

 from plants up to the master forms of the predaceous animals, there 



