
776 THE AMERICAN NATURALIST. 
a conclusion to which I do not understand the seguztur. The 
absence of mixipterygium in cladoselachids (as well as in acan- 
thodians, in fact the whole matter of the acanthodians) he does 
not consider in this connection. 
Braus, in summary, teaches that paleontological discoveries 
lead to the “overwhelming conclusion" that the recent shark 
fin has acquired its typical form of skeleton through a process 
of reduction wherein the original terminal and post-terminal 
axial portions have become lost, while the pre-axial region has 
developed and with it its basal plates. The reviewer, how- 
ever, must confess that he finds it rather difficult to determine 
exactly how Braus has obtained these paleontological results, 
unless by deriving the Devonian forms from the Permian ones, 
— which, in view of the many remarkable structural characters 
of Cladoselache (which Braus also, by the way, does not con- 
sider), appears as unconvincing as a process which derives the 
Miocene Protohippus from the Pliocene horse. 
