220 THE CARTILAGINOUS FISHES 



bears two small dorsal fins ; the caudal fin is small or altogether 

 absent. 



True Skates or Rays (Raiidce) are found principally in the 

 temperate seas. Although, on the whole, moderate-sized fishes, 

 some species are very large, measuring 7 or 8 feet across. There 

 are several British species, most of which are of value as food ; 

 they are known by various popular names, bearing more or less 

 upon some distinguishing characteristic, such as the " Painted 

 Ray," the "Starry Ray," the "Cuckoo Ray," the "Flapper 

 Skate," the " White Skate," the " Long-nosed Skate," and the 

 " Thornback," the last-named species having gained its name 

 from the spiny tubercles which stud the whole of the back. The 

 tail of the Thornback has a double row of sharp spines, making 

 it a very formidable weapon of offence, and with it the fish often 

 inflicts severe wounds on fishermen who handle it carelessly. 



Sexual differences are displayed in most species of Ray, generally 

 taking the form of differences of size or colour. In some among 

 which are the Thornbacks the male is distinguished from the 

 female by the formation of the teeth, those of the male being 

 sharp and pointed, while the female's are flattened and blunt. 



The eggs of Skates, like those of the dogfishes, are enclosed 

 in tough, horny cases. They have, however, no tendrils, but the 

 points of the four corners are drawn out into stiff, curved horns. 

 The empty egg-cases, from which the young have escaped, are 

 familiar objects on the seashore, and are often mistaken for sea- 

 weed pods. 



Many species of Ray carry electric organs at the end of their 

 tails, though these are of a more or less rudimentary nature ; 

 but the Electric Rays (Torpedinidcs) are provided with a pair 

 of well-developed electric organs situated between the head and 

 the pectoral fins, from which they are able to discharge electric 

 shocks of considerable power. With this useful apparatus the 

 rays stun their foes or the swift pelagic fishes Upon which they 

 feed. The Electric Rays differ from the majority of their allies 

 in being rounder in shape, the typical form being rhombic. They 

 haunt the warmer seas, but species are occasionally caught off 

 the British coast. 



The Sting Rays (Trygonida) are characterised by a long, 

 slender, whip-like tail armed with a sharp, barbed spine, which 



