The most characteristic feature of the Devonian age is the expansion of that new and higher class of animals, =the backboned animals=; for during the earliest Devonian or latest Silurian times the =Fishes= made their appearance. At first many of them were comparatively small in size, they were few in numbers, and of strange, unfishlike forms. Such were the _Ostracoderms_, which, though generally called fishes, belong to a type much below the true fishes, and more nearly allied to the Lampreys, for they were devoid of jaws and paired fins. There was a great variety and wealth of true fishes in the Devonian period. The _Elasmobranchii_ (Sharks) were well represented, _though very generalized ones_. _Crossopterygii_, _Dipnoi_ and _Ganoidei_ were important elements of the fish fauna of this period. At this period there was an entire absence of those highly specialized fishes (_Teleosts_) which in modern times make up the vast majority of fishes, both marine and fresh-water. The true fishes soon developed to so great an extent in size and numbers that they swarmed in the Devonian seas and quickly became the rulers of the age; hence Devonian time is known as the =Age of Fishes=. These early Devonian Fishes were of a more lowly organization than modern ones, and were what is called generalized forms; that is, they combined in themselves the characters of two distinct classes. They had distinct _amphibian characters_. From these generalized Fishes were afterwards formed, through many transitions, the _Amphibians_ and the _Fishes_ as branches from a common trunk. This illustrates what is a very general law, viz.: that the first-introduced examples of a class are not typical forms of that class, but intermediate forms or connecting links with other classes. Certain footprints recently discovered in the upper Devonian rocks of Pennsylvania indicate that the Amphibia, the lowest of air-breathing vertebrates, commenced their career in the latter part of the Devonian period; but they were inconspicuous among the monarch fishes. =Carboniferous Age.= As in the Devonian Age so in the Carboniferous times, we find flowerless plants, such as ferns, horsetails, and club mosses; but in this coal-forming age they culminate, and have become gigantic in size, especially the two latter. At this time we again meet with the next higher order of plants, as cycads, pines, cypresses, etc.