INTRODUCTION. 17 



Dr Woodward gives some striking examples of 

 this rise and fall of tribes of fishes, which may be 

 likened to the rise and fall of nations amongst 

 mankind. A certain type of fishes known as 

 the ray -finned fishes (p. 176) furnishes the first 

 of his examples. The earliest known members 

 of this type belong to a genus known as Cheiro- 

 lepis (p. 178). This appears as an isolated form 

 in the Lower Devonian fish fauna, where the 

 dominant fish are of two quite distincb types : 

 the one known as the fringe-finned (p. 176), 

 and the other as the lung-fishes (p. 25). When 

 these latter begin to decline, in the Lower Car- 

 boniferous (coal measures), " the sub-order to 

 which Cheirolepis belong suddenly appears in 

 overwhelming variety." From Cheirolepis we 

 derive our modern sturgeons. The period of 

 the Upper Permian witnesses another change. A 

 group of fishes, for the most part heavily 

 armoured, now first makes its appearance, "but 

 only a solitary genus is observed among the 

 hosts of the dominant race." In the Trias the 

 new type becomes supreme, and constitutes the 

 dominant fishes of the Jurassic period. From 

 thence onwards it gradually declined, leaving 

 but a solitary survivor in the mud-fish or bow- 

 fin of certain North American rivers (p. 183). 

 Out of the teeming hordes of the bow-fin type, of 

 the old Jurassic seas, new forms have silently 

 appeared to give battle to the old so soon as 

 they shall have gained a firm hold. These have 

 put off the old armour plate of enamelled scales, 

 and have adopted a peculiarly modern habit. 

 Many are scarcely distinguishable from the 

 B 



