464 FISHES CHAP. 



has been taken at several places in British waters. An American 

 Torpedo (Tetronarce} is represented by species on the Atlantic 

 and Pacific coasts. Narcine is a very widely distributed genus, 

 species having been recorded from the East Indies, Tasmania, 

 China, Japan, South Africa, and the Atlantic coasts of North 

 and South America. Discopyye is an eastern Pacific genus (Peru 

 and Panama). Hypnos frequents the Australian seas. 



The family seems to be exclusively Tertiary, and its earliest 

 fossil representatives are from the Upper Eocene of Monte Bolca. 



Fam, 6. Trygonidae (Sting- or Whip -tailed Kays). Disc 

 sub-rhombic, broader than long. Pectoral fins confluent with 

 the sides of the head, their preaxial endoskeletal radialia meet- 

 ing in front of the skull along the lateral margins of a slender 

 prenasal rostral cartilage. Tail usually whip-like, terminating 

 in a small caudal fin, and generally armed with a sharp, serrated 

 spine, which takes the place of a dorsal fin. Skin smooth or 

 spinose. A rectangular naso-frontal flap in front of the mouth. 

 About ten genera and fifty species. Found in nearly all 

 tropical and subtropical seas. 



Of the more important genera, Trygon (Dasyatis) is represented 

 by numerous species in the tropical parts of the Atlantic and 

 Pacific Oceans, including the Pacific coasts of North and South 

 America. Two species occur in the Mediterranean, and one of 

 them (T. pastinaca), ranges from the coasts of Norway and 

 the British Isles through the Atlantic and Indian Oceans 

 to Japan. Urogymnus frequents the Red Sea and the Indian 

 Ocean. Urolophus includes a few species of small size, distributed 

 along the Atlantic and Pacific coasts of Central and North 

 America, and in Australian seas. Pteroplatea comprises rather 

 large species, and is almost cosmopolitan in its distribution, being 

 represented by species on the Atlantic and Pacific coasts of North 

 and South America, in the Mediterranean and the Red Sea, the 

 Indian Ocean, the Malay Archipelago, and on the coasts of China 

 and Japan. The caudal spines, which may be 8 to 9 inches 

 long in some of the larger species, are capable of inflicting very 

 severe wounds, the danger of which is greatly increased by the 

 apparently poisonous cutaneous mucus introduced into the wound. 

 As the spines become lost they are replaced by others developed 

 from behind. Some Trygonidae live in fresh waters. Trygon 

 (Dasyatii) sabina frequents the streams and estuaries of Florida 



