LANCELET. 



31 



found among Fishes. In one corner are the " ganoid " scales 

 of the modern American Bony Pike (Lepidosteus), and the 

 African Bichir (Folypterus), alongside those of certain extinct 

 forms. A scale of the Tarpon, or king-of-the Herrings, illus- 

 trates thie largest development in point of size of the modern 

 " cycloid " type. Spines of the Porcupine-fish show an extreme 

 development of this kind of structure. Diagrams and spirit- 

 preparations illustrate the mode of attachment and succession 



Fig. 12. — A Jaw op the Pobt Jackson Shabk (fiestracion philippi), 

 showing sharp teeth in front and crashing ones behind. 



of fish teeth. A large series of the teeth of Sharks and Eays 

 displays the gradual passage from those of the ordinary 

 point form to others arranged in a pavement-like manner 

 and adapted solely for crushing. Both types occur in the 

 Port Jackson Shark (fig. 12), while those of some Eays 

 are solely of the pavement modification. Very remarkable is 

 the dental structure in the Parrot-fish. The west end of this 

 side of the case shows the various modifications assumed by the 

 teeth of the modern Bony Pishes ; among which, as exemplified 



