464 FISHES CHAP. 
has been taken at several places in British waters. An American 
Torpedo (Tetronarce) 1s 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. Discopyge 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 Bolea. 
Fam. 6. Trygonidae (Sting- or Whip-tailed Rays).—Dise 
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, Tygon (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. ‘T'wo species occur in the Mediterranean, and one of 
them (7. 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. Zrygon 
(Dasyatis) sabina frequents the streams and estuaries of Florida 
