DEVONIAN AND) OLD RED: PERIOD. 153 
of this group are of small size ; but few fishes, living or extinct, 
could rival the proportions of the great Dznzchthys, referred to 
Fig. 104.—Pterichthys cornutus. Old Red Sandstone, Scotland. (After Agassiz.) 
this family by Newberry. In this huge fish (fig. 102, a) the 
head alone is over three feet in length, and the body is sup- 
posed to have been twenty-five or thirty feet long. The head 
was protected by a massive cuirass of bony plates firmly articu- 
lated together, but the hinder end of the body seems to have 
been simply enveloped in a leathery skin. ‘The teeth are of 
the most formidable description, consisting in both jaws of 
serrated dental plates behind, and in front of enormous coni- 
cal tusks (fig. 102, a). ‘Though immensely larger, the teeth of 
Dinichthys present a curious resemblance to those of the exist- 
ing Mud-fishes (Lefzdosiren). 
In another great group of Devonian Ganoids, we meet with 
fishes more or less closely allied to the living Polyftert (fig. 
105) of the Nile and Senegal. In this group (fig. 106) the 
péctoral fins consist of a central scaly lobe carrying the fin- 
rays on both sides, the scales being sometimes rounded and 
overlapping (fig. 106), or more commonly rhomboidal and 
placed edge to edge (fig. 105, A). Numerous forms of these 
‘“ Fringe-finned” Ganoids occur in the Devonian strata, such 
as Holoptychius, Glyptolemus, Osteolepis, Phaneropleuron, &c. 
To this group is also to be ascribed the huge Ozychodus (fig. 
102, Zand e), with its large, rounded, overlapping scales, an 
inch in diameter, and its powerful pointed teeth. It is to be 
remembered, however, that some of these ‘“ Fringe - finned” 
Ganoids are probably referable to the small but singular group 
of the ‘‘ Mud-fishes” (zfno02), represented at the present day 
by the singular Zepzdosiren of South America and Africa, and 
the Ceratodus of the rivers of Queensland. 
Leaving the Ganoid fishes, it still remains to be noticed that 
the Devonian deposits have yielded the remains of a number 
of fishes more or less closely allied to the existing Sharks, 
