DEVONIAN AND OLD RED PERIOD. 153 



comprising the Sharks, Rays, and Chimera of the present day, 

 in which the skeleton is cartilaginous; the tail is unsymmetric- 

 ally lobed; and the scales have the form of detached bony 

 plates of variable size, scattered in the integument. 



It is to the two last of these groups that the Devonian fishes 

 belong, and they are more specially referable to the Ganoids. 

 The order of the Ganoid fishes at the present day comprises 

 by some seven or eight genera, the species of which princi- 

 pally or exclusively inhabit fresh waters, and all of which are 

 confined to the northern hemisphere. As compared, there- 

 fore, with the Bony fishes, which constitute the great majority 

 of existing forms, the Ganoids form but an extremely small and 

 limited group. It was far otherwise, however, in Devonian 

 times. At this period, the bony fishes are not known to have 

 come into existence at all, and the Ganoids held almost undis- 

 puted possession of the waters. To what extent the Devonian 

 Ganoids were confined to fresh waters remains yet to be proved ; 

 and that many of them lived in the sea is certain. It was 

 formerly supposed that the Old Red Sandstone of Scotland 

 and Ireland, with its abundant fish-remains, might perhaps be 

 a fresh-water deposit, since the habitat of its fishes is uncer- 

 tain, and it contains no indubitable marine fossils. It has 

 been now shown, however, that the marine Devonian strata of 

 Devonshire and the continent of Europe contain some of the 

 most characteristic of the Old Red Sandstone fishes of Scot- 

 land; whilst the undoubted marine deposit of the Cprniferous 

 limestone of North America contains numerous shark-like and 

 Ganoid fishes, including such a characteristic Old Red genus 

 as Coccosteus. There can be little doubt, therefore, but that the 

 majority of the Devonian fishes were truly marine in their habits, 

 though it is probable that many of them lived in shallow water, 

 in the immediate neighborhood of the shore, or in estuaries. 



The Devonian Ganoids belong to a number of groups; and 

 it is only possible to notice a few of the most important forms 

 here. The modern group of the Sturgeons is represented, 

 more or less remotely, by a few Devonian fishes such as As- 

 terosteus; and the great Macropetalichtliys of the Corniferous 

 limestone of North America is believed by Newberry to belong 

 to this group. In this fish (fig. 102, b) the skull was of large 

 size, its outer surface being covered with a tuberculated enamel ; 

 and, as in the existing Sturgeons, the mouth seems to 

 have been wholly destitute of teeth. Somewhat allied, also, to 

 the Sturgeons, is a singular group of armored fishes, which is 



