3 86 



ORDOVICIAN PERIOD 



b 



Fig. 345. ORDOVICIAN SPONGES: a, Rcceptaculites occidentalis Salter; b, 

 Brachiospongia digitata Beecher; c, Archacyathus minganensis Billings; d, Proto- 

 spongia maculosa U. and E.; e, Ischadites, species undetermined. Receptaculites 

 and Ischadites were formerly regarded as giant foraminifers. 



Cambrian sands. They are represented by burrows and by 

 teeth (Fig. 346). 



Fragmentary fossils of fishes constitute the most striking innova- 

 tion in the record of the marine life of the period. These have 



Q 6 \ 



Fig. 346. JAWS OF ORDOVICIAN ANNELIDS, highly magnified: a, Arabellites 

 cornutus Hinde; b, Glycerites sulcatus Hinde; c, Eunicites gracilis Hinde; d, Arabellites 

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



been found in a few localities only, notably near Canyon City, Colo. , 

 and in the Bighorn Mountains of Wyoming. As in the Cambrian, a 

 vast supply of unrecorded vegetation must be postulated to have sup- 

 plied food for the animals. To provide for organisms that preyed 

 upon one another in succession, from plants up to the master forms of 

 the predaceous animals, there were doubtless many species not now 

 known. The fact that vegetal tissues are not found among fossils, 

 save in rare cases, probably signifies that the bacteria concerned in 

 the decomposition of organic matter were abundant. 



General advancement. It seems clear that the adaptation of the 

 various forms of life to one another and to their physical environ- 

 ment had reached a higher stage of adjustment than in the Cam- 



