OF CREATION. 63 



The tribe of existing Placoid fishes most resem- 

 bling those whose remains are found fossil, is that of 

 which the sharks are the well-known representative. 

 These powerful and rapacious animals, which are at 

 this day the tyrants of the deep, seem to have been, 

 when first introduced, of small size, and were accom- 

 panied by some few species of the next or Ganoid 

 order. Only nine species of these shark-like mon- 

 sters have yet been determined with certainty from 

 the silurian and devonian rocks ; and of these, two 

 only are from the former. 



It is chiefly the Ganoid fishes whose remains are 

 handed down to us in the old red sandstone and other 

 rocks of that period. Sixty distinct species of these 

 fish have been mentioned, and almost all of them are 

 known from British specimens. Most of them are 

 remarkable for exhibiting strange peculiarities of 

 shape, approximating them in some intances to the 

 structure of the lower order of animals, combined with 

 some apparent affinities to the class of reptiles. 



The most remarkable group of these fishes con- 

 tains several genera, three of which will require spe- 

 cial notice. They are the Cephalaspis (or buckler- 

 headed, fig. 22), the Pterichthys (or wing fish, fig. 

 23), and the Coccosteus* (fig. 24), so called from the 

 berry-like tubercles with which its bony scales are 

 covered. 



The most extraordinary part of the first of these 

 fishes, " the buckler- headed," is the head from which 



* All these names are derived from the Greek. They are thus ob- 

 tained : Cephalaspis, KE<aA?) (cephale}, a head ; curing (aspis), a shield or 

 buckler. 2. Pterichthys, Trrepov (pteron), a wing; i^flvQ (ichthys}^ a fish. 

 3. Coccosteus, KOKKOQ (coccos), a berry; ocrrtov (osteon\ a bone. 



