PLAGIOSTOMT. 



127 



Fig. 40 gives a side view of the upper and lower jaws of the 

 " Port-Jackson shark," shewing the oblique disposition of the 

 large crushing teeth, which cover like a pavement the working 

 borders of the mouth. The anterior teeth were small and 

 pointed, (fig. 41). Behind the cuspidate teeth the five consecu- 

 tive rows of teeth progressively increase in all their dimensions, 

 but principally in their antero-posterior extent. The sharp 



Fig. 41. 

 Upper jaw and teeth of Port-Jackson Shark (Cestracion), half nat. size. 



point is converted into a longitudinal ridge traversing a con- 

 vex crushing surface, and the ridge itself disappears in the 

 largest teeth. As the teeth increase in size, they diminish in 

 number in each row. The series of the largest teeth includes 

 from six to seven in the upper, and from seven to eight in the 

 lower jaw. Behind this row the teeth, although preserving 

 their form as crushing instruments, progressively diminish in 

 size, while at the same time the number composing each row 



