FAMILY OP THE RAYS. 321 



development of the pectoral fins, which form a wide 

 salient angle at the sides, run forward completely 

 enveloping the head, and for the most part forming 

 a long conical projection in front of it. The other 

 fins are of insignificant dimensions, and generally 

 placed on the tail. The latter is armed with from 

 one to seven rows of strong spines, and is used as 

 an instrument of defence. 



In the male, the teeth, which are usually flat 

 and forming a pavement, commonly become angular 

 with age ; and that sex is further distinguished 

 by having a cylindrical appendage to each ven- 

 tral, sometimes of such length as to present the 

 appearance of three tails. The sex in question has 

 also, for the most part, a series of spines towards 

 the upper outer surface of the pectoral fins. 



As with the sharks, the females are larger than 

 the males, and the mode of propagation is similar. 

 The young are enclosed in a horny capsule of an 

 oblong-square shape, with a filament at each corner. 

 Here it is nourished by means of an umbilical bag, 

 till the due period of exclusion arrive, when it enters 

 upon an independent existence. 



Till very recently, • the Eays were regarded as 

 exclusively salt-water fish, but the discoveries of 

 Mr. Schomburgk, in South America, as well as the 

 researches of other authors, have proved the interest-i 

 ing fact that there are many kinds, particularly of the 

 sting-rays (Trygon), which are strictly fluviatile.* 



* See Naturalist's Library, Fishes of Guiana, part ii. 

 p. 175. 



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