TEETH AND SPINES. 39 



(Raja clavatci) the males have the jaws covered 

 with sharply-pointed teeth, whil-t in the females 

 they are tiny, rounded and flattened plates. 



In the Port Jackson shark (Cestracion) of 

 Australia, and in the Rliynchobatis of the Indian 

 Ocean, we have instances of the combinations of 

 teeth resulting in patterns of undoubted beauty, 

 though we must remark that this beauty is 

 entirely an accidental feature (fig. 4). 



In the first-mentioned of these two fishes ' 

 the Port Jackson shark the teeth, when seen in 

 position on the jaws, present a wonderful grada- 

 tion, beginning with a series of small spines at 

 the anterior end of the jaw, and passing back- 

 wards into large, rounded, oval seed-like bodies, 

 forming a sort of raised mosaic work. A 

 reference to the figure, p. 40, F., should make 

 this clear. In one of the rays, known under 

 the scientific name of Rhynchobatus, the 

 tooth-covered jaws are of a most remarkable 

 shape. Here the upper jaw is alternately 

 hollowed and swollen, the lower presents a 

 corresponding swelling and depressions to fit 

 into upper jaw. The teeth are uniform in 

 size. In the sting-ray (Trygori) the teeth take 

 the form of a number of A-shaped bars fitting 

 closely together, and in the eagle-ray (Mylio- 

 batis), of a number of long hexagonal bars 

 bounded on either side by rows of small teeth 

 of hexagonal form. In the comb - toothed 

 shark (Notidanus) the teeth have many cusps 

 or tiny comb-toothed-like processes along the 

 cutting edge, hence its name. In the shark's 

 teeth, by the way, we meet with a great range 



