FISHES ABUNDANT. 



ing a powerful development of sharp conical teeth situated 

 on the margin of the jaws. One genus, the koloptychiuSj in- 

 troduced near the close of the Devonian era, and passing up 

 into the next, presents a flat oval form, measuring in one 

 specimen thirty inches by twelve, with a covering of strong 

 plates, wavily grooved and overlapping each other, the head 

 forming only a slight rounded projection from the general 

 figure. We here find another early and startling example, in 

 addition to the brontes, of animals which may be called large. 

 In the strata of this formation at Dorpat, there are gigantic 

 bones, which were at first thought to belong to reptiles, but 

 have since been ascertained to be remains of fishes, leading to 

 the conjecture that the animals to which they appertained could 

 not be less than thirty-six feet long. 1 



M. Agassiz has announced nine genera of sharks of the 

 division Cestracion in the Devonians of Russia. It is in this 



FIG. 24. 



Lower Jaw and Teeth of Cestracion Philippl, or Port- Jackson Shark. 



voracious family that we see the placoids represented in modern 

 seas ; the ganoids are all but unrepresented in our time. Of 

 both classes, one invariable peculiarity has attracted much 



1 The head fountain of information on the early fishes is M. Agassiz's 

 Poissons Fossiles, a splendid but not readily accessible book. For more 

 popular descriptions, reference may be made to New Walks in an Old 

 Field, by Hugh Miller, and to Jameson's Journal, July and October, 

 1844. See also the excellent manual of Professor Ansted. 



