DEVONIAN ANIMALS. 



335 



osts — did not then exist. The Devonian fishes were all Ganoids and / 

 Placoids, especially Ganoids. 



We have said some were of great size. The Dinichthys (Fig. 423) of 

 the Ohio Devonian, according to Newberry, was at least eighteen feet 



long and three feet thick. A ^ ^ 



specimen of Titanichthys recent- ..,-••• — j^^Tl ^^*\. 



ly found was nearly six feet 



across the head (Claypole), and 



with orbits of eyes three inches 



in diameter. The animal could 



hardly have been less than thirty 



feet long. The Onychodus (Figs. 424-426) was twelve to fifteen feet 



in length, and had jaws two feet long, armed with teeth two inches 



Fig. 423. — Jaws of Dinichthys Terrelli, x 25 (after 

 Xewberry). 



Fig. 424. 



Fig. 425. 



Fig. 426. 



Figs. 424-426.— Onychodus sigmoides (after Newberry): 424, Scale, natural size; 425, a Tooth, 

 natural size ; 426, a Row of Front Teeth, reduced. 



long. We have said also that they were many of them armed, espe- 

 cially for defense. All Ganoids, but especially Devonian Ganoids, were 

 covered with an impenetrable coat of mail, composed of thick, closely- 

 fitting, bony, enameled scales or plates. We are indebted to this fact 

 that their external forms are often so well preserved ; for their skele- 

 tons were wholly cartilaginous, and therefore unsuitable for preserva- 

 tion. The Placoids, on the other hand, had neither bony skeleton nor 

 bony scales. We know them, therefore, only by their teeth and by cer- 

 tain spines supporting their fins. The Ganoids are, therefore, the more 

 interesting. 



Characteristic Examples of Devonian Fishes. — The Cephalaspis 

 (Fig. 427) and Pteraspis (Fig. 428) are among the earliest and most 

 curious forms. The former was a small fish, seven or eight inches 

 long, with a broad head, shaped somewhat like the head-shield of a 

 Trilobite, and covered with bony, enameled plates ; and body covered 

 with rhomboidal ganoid scales. In the Coccosteus and Pterichthys 

 (Figs. 429 and 430) the large, close-fitting, immovable plates covered 

 not only the head but the anterior portion of the body. The huge 



