LANCELET. 
31 
found among Fishes. In one corner are the ganoid " scales 
of the modern American Bony Pike (Lepidosteus), and the 
African Bichir (Polypterus), alongside those of certain extinct 
forms. A scale of the Tarpon, or king-of-the Herrings, illus- 
trates the 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 of The Port Jackson Shark (Cestraeion pliilippi'), 
showing sharp teeth in front and crushing ones behind. 
of fish teeth. A large series of the teeth of Sharks and Pays 
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 Pays 
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 Fishes ; among which, as exemplified 
