2 9 i6 SHARKS AND RAYS 



They progress slowly by means of the pectoral fins, the broa^ and thin margins of 

 which are set in an undulating motion, entirely identical with that of the dorsal and 

 anal fins of the Pleuronedida. Like the sharks, they are exclusively carnivorous, 

 but being unable to pursue and catch rapidly moving animals, they feed chiefly on 

 mollusks and crustaceans. The color of their integuments assimilates, however, so 

 closely to that of their surroundings, that other fishes approach near enough to be 

 captured by them. The mouth of the rays being entirely on the lower surface of 

 the head, the prey is not directly seized by the jaws; but the fish darts over its vic- 

 tim so as to cover and hold it down with its body, when it is conveyed by some 

 rapid motions to the mouth. Rays do not descend to the same depth as sharks; 

 with one exception, none are known to have been caught by a dredge working in 

 more than one hundred fathoms. The majority are coast fishes, and have a com- 

 paratively limited geographical range, none extending from the northern into the 

 southern temperate zone. Some of the eagle rays are, however, more or less pelagic, 

 although when these are met with swimming in the open sea it is probable that shoal 

 water exists at no great distance. As may be observed in many of the lochs on the 

 west coast of Scotland, where these loathsome creatures may be seen flapping lazily 

 alone at the bottom of the clear water, skates and rays are more or less gregarious 

 fishes. They frequently arrive suddenly on oyster beds, to the dismay of the 

 owners, where they appear to remain so long as any of the mollusks are obtain- 

 able.. Writing of the species armed with caudal spines, Day observes that they "lie 

 concealed in the sand, and are reputed to be able to suddenly encircle fish or other 

 prey swimming above them with their long whip-like tails, and then wound them 

 with their serrated tail spines." Many rays ascend rivers to considerable distance, 

 and some kinds, especially in tropical America, are exclusively inhabitants of fresh 

 waters. Nearly all lay eggs. 



To illustrate the typical genus, which is represented by about a 

 18 dozen species from the warmer seas, we take the halavi ray (Rhino- 

 batis halavi) , which ranges from the Mediterranean and the coasts of Western Africa 

 to China. In these fishes the depressed body passes imperceptibly into the tail; the 

 muzzle is produced into a long beak, the space between which and the pectoral fin 

 is occupied by a membrane; and the wide nostrils are oblique, with their front valves 

 separate. The blunt teeth are marked by an indistinct transverse ridge; the dorsal 

 fins, which are situated far behind the pelvic pair, have no spines; and the caudal 

 has no lower lobe. Fossil species are found from the Tertiary to the upper Jurassic. 

 The .allied Australian genus Trigonorhina differs in having the front nasal valves 

 united, and forming a broad quadrangular flap. 



The third genus of the family, which is represented by two species 

 from the coasts of the tropical portions of the Indian Ocean, differs in 

 that the first dorsal fin is placed above the pelvic pair, in the presence of a lower 

 lobe to the caudal, and also in the form of the dental plate, which is deeply undu- 

 lated, so that the prominences of one jaw fit into hollows in the opposite one; the 

 individual teeth being more or less diamond shaped. These rays do not exceed 

 eight feet in length. Several extinct genera occur in the upper Jurassic strata of 

 Europe. 



