THE CARTILAGINOUS FISHES 219 



long-bodied sharks, and the rays, with their broad, flat bodies 

 and sluggish ways. The two families approximate one another 

 very nearly, but from the position of the gill-clefts the Saw-fishes 

 have been placed by zoologists in the first sub-order of the Elas- 

 mobranchs (Selachii), and the True Saw-fishes in the second sub- 

 order (Batoidei). In the Saw-fishes the gill clefts are lateral (or 

 placed at the side), as in the majority of the sharks ; while the 

 True Saw-fishes have ventral gill-clefts ; that is to say, they are 

 situated on the under side of the body, as is the case with all rays. 



Both Saw-fish families are distinguished by the curious long, 

 flattened beak or rostrum a prolongation of the upper jaw, set 

 along each edge with a series of sharp, pointed teeth, giving this 

 formidable weapon the appearance of a double-edged saw. In 

 shape the Saw-fishes more nearly approach the sharks than the 

 rays, but the body of a True Saw-fish is somewhat depressed. 

 They differ, too, in size, the Pristio^phondce being comparatively 

 small, while the Pristidcs are often very large. True Saw-fishes 

 are most plentiful in the tropic seas ; they are huge creatures, often 

 armed with " saws " quite 6 feet long, while the entire length of the 

 fish may be 20 feet or more. Like the sharks, the Saw-fishes are 

 carnivorous, and they kill their prey by striking sideways at it 

 with the terrible " saw," afterward ripping and tearing the body 

 with the sharp-toothed edges and swallowing the severed pieces. 

 A blow from such a powerful weapon is naturally a very serious 

 affair, and some Indian species of Saw-fishes that ascend rivers 

 for considerable distances are a constant source of danger to bathers. 



Rays or Skates are for the most part sluggish fishes, frequent- 

 ing the shallow waters round the coast. They are ground-fishes, 

 and seek their food, which consists of Crustacea, molluscs, and small 

 species of fishes, at the sea-bottom, over which they move slowly 

 by lazily flapping their huge pectoral fins with a gentle wave-like 

 motion. A typical Ray is very broad and flat, and as it lies half 

 buried in the sand beneath the water it is exceedingly difficult to 

 distinguish it from its surroundings, for, although the under 

 surface is usually white, the back of the fish is almost invariably 

 coloured to harmonise with its environment. This protective 

 coloration is the rule with all fishes of sluggish habits fre- 

 quenting the bottom of the sea. The pectoral fins are enormously 

 expanded ; the tail is long, slender, and whip-like, and usually 



