416 



RAIIU^f;. 



that on the right, an inside view of one-half of the mouth of 

 an equally adult female of the Thornback Ray. While both, 

 are young, the teeth in both sexes are alike broad and flat ; 

 but as the male acquires age and sexual power, the teeth that 

 are nearest the centre begin to alter in form and become 

 pointed, as will be seen on close examination, by an elonga- 

 tion of the internal angle ; all the points being directed back- 

 wards or towards the throat. Some exceptions to this appa- 

 rent rule will be pointed out. 



Another sexual peculiarity in which the Skate resemble 

 the Sharks is the cylindrical appendage to each ventral fin in 

 the males. The figure at the head of this subject is taken 

 from the under surface of a female, in which no appendages 

 exist : the second figure of the true Skate, the next in suc- 

 cession, is from the under surface of a young male, and small 

 appendages lying on each side close to the tail may be seen ; 

 and even in very young specimens, not more than three 

 inches in breadth, the sexes may be determined by the 

 constant existence of these appendages in the males. The 

 figure of the third species is taken from the upper surface of 

 an adult male, and exhibits these appendages of much 

 greater length : their use may be inferred from the name 

 they bear — they are usually called claspers. This third figure 

 of the Sharp-nosed Ray exhibits also other peculiarities com- 

 mon to males : these are the clusters of spines outside the 



