TEETH AND FOOD 



23 



types of teeth may occur in the same jaw. In the primitive 

 Comb-toothed Sharks [Hexanchidae) the teeth of the upper jaw 

 are for the most part provided with a large central cusp or 

 point with several smaller cusps on either side, but in the 

 lower jaw each consists of several pointed cusps, graduated in 

 size, all inchned in the same direction, and supported on a 

 long basal plate (Fig. 52c). Teeth with three or more cusps 

 probably owe their origin to the fusion of several of the primitive 

 single teeth. In certain Sharks the denticles covering the body 

 tend to be aggregated together in groups, perhaps three in a 

 row, forming a plate armed with a Uke number of spines, and 

 it seems likely that 

 similar fusions have 

 taken place in the 

 jaws, but always of 

 denticles lying side by 

 side. In the Great 

 White Shark or Man- 

 eater {Carcharodon) , 

 one of the most for- 

 midable of all the 

 Sharks, the teeth are 

 very powerful, flat- 

 tened, triangular in 

 shape, and with the 

 edges finely serrated 

 (Fig. 52a). This 

 Shark grows to a 



Fig. 52. SHARK TEETH. 



«. Tooth of Great White Shark or Man-eater 

 length of about thirty (Carc/zaroJow rondeleti),X \ ; b. Of Tiger Shark 

 feet, but, judging {Gakocerdo tigrinus) X f ; c Of Comb-toothed Shark 

 r ^u ^\rZ. c.;?^ r^f (Hexanchus gnseus), x f ; d. Of Sand Shark (Odon- 



from the large size ot ^^^^-^ ^^^,^,)^ ., s., 



some fossil teeth of a 



similar kind which have been discovered. Man-eaters of truly 

 colossal size must have inhabited the seas in past times. A 

 tooth six inches in length must have belonged to a Shark at 

 least ninety feet long, and such monsters probably survived 

 until comparatively recent times, for the Challenger Expedition 

 dredged some of their teeth from the bed of the Pacific Ocean. 

 The Tiger Shark {Galeocerdo) , another large species found in 

 nearly all warm seas, has teeth of a very peculiar shape, each 

 one being flat and sickle-shaped, with a fluted edge suggesting 

 that of a patent bread-knife, and with a triangular point at the 

 summit which projects obliquely outward (Fig. 52b). 



