DEVONIAN FAUNA. 149 



The vertebrate life of this period exhibits a remarkable develop- 

 ment as compared with that of the period preceding. But, as in 

 the latter, all the remains belong to the class of fishes, and indeed 

 principally, or one might say almost exclusively, to the same two 

 orders, the elasmobranchs and ganoids. No animal of a grade 

 higher than fishes had as yet appeared upon the scene, or, if possi- 

 bly it had, no traces of it have thus far been discovered to indicate 

 its existence there. To such an extent was the fish-fauna developed 

 that the term " age of fishes" has not inappropriately been applied 

 by paleontologists to designate this gpoch of geological time. The 

 preponderating types are the ganoids, which appear not only in 

 forms that may be considered more or less remotely related to the 

 type of the modern sturgeon (Macropetalichthys), or to the fringe- 

 finned Polypteri of Africa (Koloptychius, Glyptolepis, Dipterus, 

 Osteolepis), and the American alligator-gars (Chirolepis), but in 

 ouch as have no representatives in any of the succeeding formations. 

 These are the so-called "bucklered ganoids," which, in addition to 

 the enamelled plates characteristic of this group of fishes, had the 

 head and the anterior portion of the body encased in bony plates, 

 more or less firmly united to each other, and serving as a protective 

 armour. To this group, among others, belong Pteraspis, Cepha- 

 laspis, Pterichthys, and Coccosteus, forms which had their forerun- 

 ners already in the Upper Silurian deposits. Generally placed among 

 the ganoids, and closely related to Coccosteus, are the giant Dinieh- 

 thys and Titanichthys, which appear to have attained a length 

 of from twenty to thirty feet, and whose dental apparatus closely 

 approximates that of the modern Lepidosiren, one of the lung-fishes 

 (Dipnoi), a group of animals which effect a transition between the 

 true fishes and the amphibians. If this relationship with Lepido- 

 siren be absolutely established, as is claimed to be the case by many 

 of the more prominent anatomists, then it is certainly significant that 

 the advent of the Amphibia (the class of animals immediately above 

 the fishes), in the succeeding Carboniferous period, is preceded by 

 just that group which, in accordance with the principles and work- 

 ings of evolution, we should expect to find interposed — the group 

 which, on the one hand, combines some of the characters of the 

 Amphibia, and, on the other, those of the ichthyic fishes. But, 

 whatever the exact relationship of Dinichthys may be, there can be 

 little question as to its representing a dipnoan type, or at least a 



