44 
HAROLD’S DISCUSSIONS. 
newcomers, we conclude that tliej must have been 
genuine fighters, and doubtless there were great bat¬ 
tles fought in those waters. 
It must not be supposed, however, that fishes were 
the only animals living during this age. Many of 
the invertebrate forms continued their existence. 
The brachiopods and cephalopods increased in size 
and number of species, but the trilobites diminished 
in both. A species of the ammonite cephalopods 
came in during the latter part of the period, and 
reached its highest development in the age of reptiles. 
Fig. 25.—A type of Devonian fishes. 
This cephalopod looked like a large sausage, larger 
at one end than at the other. It resembled the 
straight-chambered orthoceratite, except that it was 
rolled in a coil wliich was curiously divided on the 
inside into chambers. The shell had horny projec¬ 
tions on top, but was smooth and pearly beneath. It 
was, in fact, a higher form of the Silurian nautiloids 
(see Fig. 21). 
Fishes introduced another type of animal life— 
vertebrates—a class to which man himself belongs, 
namely, the back-boned animals. 
The earth was, no doubt, clothed with verdure; 
flowering plants and deciduous trees were still absent. 
