674 



GEOLOGY 



tion seems to have lasted from the later part of the preceding 

 period, until well into the Triassic. 



The Permian record of the arthropods and of the terrestrial 

 mollusks is very poor, and probably represents an impoverished 

 state of these classes, but local exceptions will doubtless yet be 

 discovered. 



III. The Fresh-water Life 



The amphibians and some of the reptiles constituted, in a sense, 

 a portion of the fresh-water as well as the land life. Besides these, 

 fishes were abundant, locally at least On the whole they had a 

 rather modern aspect. 



Fig. 462. Pareiasaurus serridens, Karoo formation, Cape Colony, S. Africa; 

 X about 1-25. (After Broom.) 



There were fresh-water mollusks, some of which resembled 

 unios. The arthropods, so far as known, show but little change 

 from those of the preceding period. 



IV. The Marine Fauna 



The withdrawal of the epicontinental seas from considerable 

 portions of the continents reduced the territory availal le for shallow- 

 water sea life, and of such life there was a uTeat reduction. It is i<> 

 be noted that this reduction came at a time when conditions were 

 unfavorable for land life (p. 669). In North America the restricted 

 marine fauna lived in tracts just previously occupied by the 



