194 PALEOZOIC FISHES OF NORTH AMERICA. 
Sharks are so numerous as to show that Elasmobranch fishes were much 
more abundant in the Carboniferous sea than in those of the present or-any 
other geologic age. The exception to the rule of the domination of the 
Sharks offered by the Ganoids discovered by Mr. McAdams is therefore of 
special interest, and we can see in the evidence furnished by their jaws and 
teeth that they were quite capable of contending successfully against any 
of their Elasmobranch antagonists; indeed, none of the Sharks yet known. 
to us as inhabitants of the Carboniferous sea were provided with a dental 
armament as formidable as that of Celosteus or Rhizodus. The largest 
of the Carboniferous Elasmobranchs, Archeobatis gigas, Orodus ramosus, 
Psammodus grandis, and P. plenus, had crushing teeth, and doubtless lived 
upon mollusks, crustaceans, and crinoids, while the species with cutting and 
piercing teeth, Petalodus and Cladodus, were much less formidably armed 
than Rhizodus. 
In the fish fauna of the Devonian age the great Crossopterygian scaled 
Ganoid Onychodus stood out in strong contrast to the number of large and 
small Placoderms with which it was associated, and it is interesting to note 
that in the Carboniferous sea another large and formidable Crossopterygian, 
Rhizodus, contrasts equally with the crowd of Elasmobranchs. We may 
even suspect that in each case the Ganoid was the most formidable, since 
with very powerful dental weapons he must have had a flexible scaled body 
that would allow of greater celerity, and while Onychodus would have been 
no match for Dinichthys if once within the grasp of its massive Jaws, it 
could easily avoid them, and with its projecting intermandibular teeth 
two or three inches in length could have lacerated the exposed portions 
of the body quite at his leisure. So Rhizodus, with a gape of perhaps two 
feet, and jaws set with laniary teeth three or four inches in length, if he 
had the address to avoid the formidable dorsal and pectoral spines of 
the Sharks, would have found their shagreen-covered bodies easily pene- 
trable. 
