Tlie Coming of Vertebrates and Rise of Fishes 



from different parts of the jaw are often quite 

 unlike, so that teetli from a single shark may 

 receive several names. And there is no way 

 of finding out these mistakes save by the rare 

 and fortunate discovery of some unusually well- 

 preserved specimen having the teeth and spines 

 in place. These sharks were none of them large 

 as sharks now go, but what was lacking in size 

 was more than made up in numbers, for in a 

 short time — short geologically — after they were 

 faii'ly established they became the leaders among 

 living things. During the Lower Carbonifer- 

 ous period sharks were more numerous both as 

 regards s]3ecies and individuals than before or 

 since ; nearly 300 species have been described 

 from the rocks of that period, although but 

 167 are from North America, while teeth and 

 spines are abundant. 



The history of the sharks is peculiar, and 

 their fall as rapid as their rise ; by the time the 

 Permian, which overlies the Carboniferous, was 

 reached they had dropped to 10 species abroad 

 and 9 in this country ; and while they recov- 

 ered in a measure from this abrupt descent 



109 



