on the Fossils of the older Deposits in the Rhenish Provinces. 333 



most ancient traces of fishes known to us are not found below the lowermost 

 Ludlow beds, in which remains of the Pterygotus problematicus have been found ; 

 in the upper beds the species are more common and their characters better defined. 

 The genera Onchus, Sclerodus, Plectrodus, Thelodus and Sphagodus mark this zone ; 

 but it was in the Devonian period that the animals of this class really took posses- 

 sion of the seas. In Scotland, in the west of England, in Courland, Livonia and 

 Lithuania, the Devonian beds contain numerous remains of those remarkable lori- 

 cated fishes, such as the Holoptychius and the Coccosteus, or of such as are furnished 

 with aliform appendages or extraordinary fins, as the Pterichthys and other allied 

 Ichthyohtes. The genera Cephalaspis, Osteolepis, Cheirolepis, &c., are not rare in 

 the old red sandstone of England and Scotland. The most extensively distri- 

 buted fish of this period was the Holoptychius nobilissimus , which is found not only 

 in all those countries we have mentioned, but also in the centre of Russia in Eu- 

 rope and even in Pennsylvania, associated with a Megalichthys in beds of the same 

 age. A species of Coccosteus is also noticed in North America. 



Fishes have also lived in great numbers during the coal period : thus the coal- 

 measures of Sarrebruck have produced the genera Acanthassus and Amblypterus ; 

 those of Shrewsbury, Coalbrook Dale and Titterston Hill have furnished the 

 Ctenodus, Megalichthys, Gyracanthus, Ctenacanthus, &c. The Holoptychii seem to 

 pass up from the middle system into this ; and Palcsoniscus, of which the species 

 are abundant enough in the coal-measures of the United States, lived also in the 

 epoch of the zechstein (magnesian limestone or Permian system), a circumstance 

 which further tends to unite zoologically this last-mentioned deposit with the true 

 Palaeozoic rocks. Not a single species of fish has hitherto been noticed in any 

 two systems. 



Notwithstanding the importance of the class, we can give only this general 

 view of it ; the slight special acquaintance we have with the animals which com- 

 pose it not permitting us to give a more complete idea of the actual state of 

 science in relation to them. 



Recapitulation. — The Fauna of the Palaeozoic rocks with which we are now ac- 

 quainted, thus presents 326 genera, containing 2698 species, of which 807 are 

 Silurian, 984 Devonian, and 1072 Carboniferous : 1 13, or rather more than i^th, 

 are common to the first and second systems ; 79, or ^th, are common to the se- 

 cond and third systems ; and 15 only, or yrs^rd, range through the entire series of 

 ancient formations. This latter proportion, being -f^nd, if we regard the species 

 pointed out in the Silurian and Carboniferous systems, will also be found in the 

 Devonian. There are 177 species more in the middle system than in the lower, 

 and 88 more in the upper than in the middle system. 



The details we have j ust given of the animalization of the ancient seas during a 



VOL. VI. SECOND SERIES. 2 X 



