THE LOWER FISHES 



143 



turn on the swimmer. To draw a shark's blood in the water would be 

 most foolish. This would only serve to incite this shark and draw others to 

 the scene. 



Under water, sharks possess a puzzling mixture of ferocity and timidity. 

 Their large size, abundance in shallow and comfortably warm waters, and the 

 many unknown facets of their behavior make them ideal subjects for observation 

 and study. With the elimination of doubt, overconfidence, and hysteria, the 

 underwater swimmer is in the unique position of being able to study these 

 creatures firsthand. 



The Primitive Sharks 



There is but one family of these protoselachians ("shark forerunners") 

 remaining in the seas today. It is the sole survivor of the ancient stock that 

 gave rise to modern sharks and is distinguished from them in its primitive jaw 

 suspension, dentition, and other anatomical characters. 



PORT JACKSON SHARKS: Family Heterodontidae 



The Latin name of the family refers to the fact that the teeth are of two 

 kinds; those in the front of the mouth are small and pointed for grasping and 

 those in the back are flattened like molars for crushing. There are two large 

 dorsal fins, both preceded by a stout spine. The family contains only one genus 

 of wide distribution, but not occurring in the Atlantic. 



Fig. 49. Port Jackson shark. 



