616 



GEOLOGY 



Among mollusks, pelecypods (Fig. 433) were rather abundant, 

 and in some of the sandy and silty beds predominated. Some of 

 them still retained a Devonian aspect, and those in the Indiana 

 foraminiferal limestone were diminutive, like the brachiopods. 

 Gastropods were more diversified than in the Osage fauna, and some 

 Devonian genera which had apparently been absent from the 

 Osage reappeared. The cephalopods (Fig. 433) also were more 

 abundant than they had been in the Osage. Trilobites were almost 



Fig. 434. Cladoselache fyleri Newb. Restoration by Dean. About one- 

 fifth natural size. From Cleveland Shales, Ohio. Often referred to the 

 Devonian. 



unknown, and the other crustaceans left an unimportant record. 

 Sharks were important and other fish were present. 



The most striking peculiarity of the fauna, it may be repeated, 

 resulted from the invasion of the more conservative fauna of 

 Devonian aspect from the sea of the Great Basin, and perhaps from 

 a similar incursion of lingering forms from the Waverly gulf on the 

 east. The remarkable thing is that these should have succeeded, 

 so far as they did, in impressing themselves on the composite result , 

 and in giving tone to the whole. It is more natural to expect an 

 antiquated fauna to be overwhelmed by a younger and more pro- 

 gressive one. It would be interesting to know what happened from 



