38 American Fisheries Society 



(Cestracion zygaena) a transition to the paved type of 

 teeth may be noted. The teeth of the two dogfishes com- 

 mon to our coast are very unlike. In the spiny dogfish 

 (Squalus acanthias) , they are compressed, with a distinct 

 cutting edge; in the smooth dogfish (Galeorhinus l&vis), 

 they are blunt, in pavement. 



Certain of the rays have powerful crushing jaws which 

 are capable of breaking the thick shells of clams and 

 other mollusks upon which they feed. The paved teeth 

 of the cow-nosed ray (Rhinoptera quadriloba) and the 

 spotted sting-ray (Aetobatus narinari) are well fitted for 

 this purpose, and the functioning teeth of these are usual- 

 ly very much pitted and worn by such use. The spotted 

 sting-ray, which reaches a length of 12 feet or more, 

 feeds almost entirely on clams, which it digs from the 

 natural beds. The specimen from which the jaws, which 

 I will show you, were taken was 9 feet, 6 1 /-. inches long. 

 The stomach of this specimen contained a considerable 

 quantity of the meats of clams without any pieces of the 

 shells. As much as a gallon of clams is stated to have 

 been taken from the stomach of a single individual and 

 no pieces of shell were found. A surprising degree of 

 specialization is revealed to us, as shown by the ability 

 of this species to dig the clams, to crush or open the shells 

 and separate the meat from the shells. 



In some of the rays the teeth differ according to sex, 

 those of the female being blunt, while those of the male 

 are sharp pointed, in some cases almost needle-like. We 

 find such differences in the barn-door or smooth skate 

 (Raja stabuliforis) , in some of the sting-rays, of which 

 Dasybatus hastatus is an example, and in the small devil- 

 fish (Mobula hypostoma). 



A microscopic examination of the armature of the skin 

 of different species of sharks and some of the rays, will 

 disclose as great variation in the form of these defenses 

 as have been found in the teeth. When these calcified 

 papillae are small and close set, they are referred to as 

 dermal denticles, and the skin is called "shagreen." In 

 some cases they are larger, taking the form of tubercles, 



