186 THE STORY OF FISH LIFE. 



numbers as to fill the shad-nets, and thus render 

 that fishery impracticable for many days. In 

 the formation of the vertebral column Lepi- 

 dosteus is unique, being the only fish in which 

 the vertebrae are connected by cup and ball 

 articulations. 



Concerning the actual descent of the more 

 modern fishes, we have much yet to learn. But 

 the general model upon which the most familiar 

 of our existing forms was shaped appears as far 

 back in time as the Upper Triassic formations. 

 Some of the fishes of this period, Dr Woodward 

 tells us, differ only from such groups as the her- 

 ring tribe in the more primitive form of the 

 backbone, which was only imperfectly ossified, 

 in the presence of peculiarly shaped scales at the 

 base of the fins, known as " fulcra," characteristic 

 of the older so-called "ganoids" such as the 

 sturgeons, and in the possession of the thick 

 enamel-coated scales known as "ganoid." These 

 are the models which time and evolution have 

 changed into the herrings, salmon, pike and 

 perch, and so on, of to-day. 



The tropical and sub-tropical Elops is one of 

 the most ancient of living fishes of the modern 

 type. Like the sharks, and many other primitive 

 forms, its intestine is provided with a spiral 

 valve to be quite correct, in elops there is a 

 vestige of this valve. Furthermore, it bears 

 another badge of lowly origin in the shape of a 

 bony plate beneath its jaws the gular plate; 

 in this respect it resembles the bow-fin and its 

 allies. 



The herrings form another group of ancient 



