SAU110ID FISHES. 69 



by their strength and magnitude, seem as if they might have 

 served for the armour of a Crocodile ten times the size of the 

 fish. Its head, also, was inclosed within bony plates, whose 

 upper surface was covered with rough tubercles of enamel ; and 

 the jaws, likewise, were composed of bone, whose outer surface 

 was polished, covered with enamel, and unclothed with skin. 

 A row of thickly-set pointed teeth fringed the enamelled edges 

 of the mouth, and corresponded to the lips of ordinary fish ; 

 whilst within this was a second and wider range of teeth, 

 at least twenty times the bulk of the others. This, and some 

 other allied genera, were evidently the " pirates " of their day ; 

 the extraordinary armature of their jaws being in conformity 

 with the remarkable defences, with which the bodies of the fishes 

 that served for their prey were endowed. 



588. As we pass from the Old Red Sandstone into the newer 

 rocks, we meet with a change in the characters of the Fish, 

 whose remains are imbedded in them. All those just described, 

 with the exception of the last, disappear ; and they are replaced 

 by others. Still we find that of the Fish contained in the 

 Mountain Limestone and the beds associated with it, a large 

 proportion belonged to the order Ganoidians ; but, among these, 

 the Sauroid fishes now predominate. These are at once dis- 

 tinguished by the peculiar form of their teeth ; which are 

 marked by longitudinal furrows like those of Crocodiles ; and 

 which have a conical hollow at the base, in which the next 

 tooth is prepared, as in many Reptiles. So strong, indeed, is 

 the resemblance of both the teeth and scales of several of the 

 Fishes of this group to those of some Crocodilian animals, 

 that, when first discovered, they were immediately referred to 

 that class. The dimensions of the teeth of the genus Megalic- 

 thys (large fish), far exceed those of any other fishes' teeth that 

 have been yet examined ; one of them having been found to 

 measure nearly four inches in length, with a breadth at the base 

 of nearly two inches. The large teeth are accompanied by 

 several very small ones, which alternated with them, and were 

 distributed over the whole of the inside of the mouth. Scales of 

 this fish have been met with as much as five inches in diameter. 



