120 FISHES. 



traces of undoubted fishes. The earliest of these, in Britain, 

 is found in the base of the Ludlow rocks (Lower Ludlow 

 Shale), and belongs to the placoganoid genus FUras'pis. 

 Also in the Ludlow rocks, but at the summit of their upper 

 division, are found fin-spines and shagreen, probably belong- 

 ing to Cestraciont fishes — that is to say, to fishes of as high 

 a grade of organisation as the Elasmohrayichii. In the Upper 

 Silurian of Europe various remains of fishes have likewise 

 been found ; but this formation in America has as yet 

 yielded no fish-remains. So abundant are the remains of 

 fishes in the next great geological epoch — namely, the De- 

 vonian or Old Eed Sandstone — that this period has fre- 

 quently been designated the " Age of Fishes." Most of the 

 fishes of the Old Eed Sandstone belong to the order Ganoidei, 

 while the order Bijmoi is now represented for the first time. 

 In the Carboniferous and Permian rocks, which close the 

 Palseozoic period, most of the fishes are still Ganoid, but the 

 former contain the remains of many Plagiostomous fishes. 

 At the close of the Palteozoic and the commencement of the 

 Mesozoic epoch, the Ganoid fishes begin to lose that predomi- 

 nant position which they before occupied, though they con- 

 tinue to be represented through the whole of the Mesozoic 

 and Ivainozoic periods up to the present day. The Ganoids, 

 therefore, are an instance of a family which has endured 

 through the greater part of geological time, but which early 

 attained its maximum, and has been slowly dying out ever 

 since. Towards the close of the Mesozoic period (in the 

 Cretaceous period) the great order of tlie Teleostean or 

 Bony fishes is for the first time known certainly to have 

 made its appearance. The orders of the Marsipohranchii 

 and Phnryngohrancliii have not left, so far as is known, any 

 traces of their existence in past time. Judging from an- 

 alogy, however, it is highly probable that the two groups last 

 mentioned must have had a vast antiquity, and in this connec- 

 tion we must briefly consider the extraordinary little fossils 

 which are known as " Couodonts." These bodies were first 

 discovered by Pander in the Silurian and Devonian of 

 Eussia, and numerous forms of them were described and 

 figured by him in his great work on the fossil fishes of that 



