TOSSIL nsHES. 453 



that which characterises this group in our island, containing 

 fishes of the genera Holoptychius, Coccosteus, Diplopterus, 

 &c., associated with mollusca of the same genera as those 

 found in the Devonian rocks in Western Europe. 



The Devonian group is well developed in the United 

 States at the Falls of the Ohio. At Louisville, in Kentucky, 

 Sir Charles Lyell * states that " there is a grand display of 

 one of the limestones of this period, resembling a modern 

 coral reef. A wide extent of surface is exposed in a series 

 of horizontal ledges, at all seasons when the water is not 

 high ; and the softer parts of the stone having decomposed 

 and wasted away, the harder calcareous corals stand out in 

 relief, and many of them send out branches from their erect 

 stems, precisely as if they were living. Among other species 

 large masses, not less than five feet in diameter, of Favosites 

 gothlandica were observed, with its beautiful honeycomb' 

 structure well displayed ; and, by the side of it, the Favis- 

 tella, combining a similar honeycombed form with the star 

 of the Astrcea. There was also the cup-shaped CyatTio- 

 pliyllum, and the delicate net-work of the Fenestella, and 

 that elegant and well-known European species, the 'chain 

 coral,' Catenipora eschar aides, with a profusion of others. 

 These coralline forms were mingled with the joints, stems, 

 and occasionally the heads, of encrinites." 



FOSSIL FISHES. The most prevalent organic remains 

 contained in the subdivisions of this group in Scotland 

 consist of fossil fishes, belonging to the genera Holoptychius, 

 Cephalaspis, PtericJitTii/s, Coccosteus, Diplopterus, Dipterus, 

 and CJieir acanthus. Eight species of Pterichthys (or winged 

 fish) are known. Fig. 192 represents the under-surface of 

 one of these. The singular fins, with their strong points 

 and oar-like blades, were weapons of defence, which, like 

 the occipital spines of the river bull-head {Coitus gobio), 

 were erected in moments of danger or alarm, and at others 

 lay close to the creature's side ; the tail being the sole 

 instrument of motion. 



The genera Dipterus and Diplopterus are thus named, 

 because their two dorsal fins are so placed as to front the 

 anal and ventral fins, and appear like two pairs of wings. 



[ * Manual of Elementary Geology, Third Edition, p. 349. 



