520 PISCES SUB-CLASS IV.ELASMOBRANCHII. 



teeth. In the second genus, of which various members range through all 

 the warmer seas, the gill-slits are placed on the inferior aspect, and there 

 are no tentacles to the saw. Saw-fishes of this genus grow to twenty feet 

 or more in length, when their offensive weapon may measure as much as 

 a couple of yards. They are some of the most terrible and cruel members 

 of the whole order, using their formidable saw for the purpose of ripping 



open the bodies of their victims 

 by a lateral stroke, and then 

 feeding greedily on the in- 

 testines and torn flesh. Even 

 bathers in fresh waters are by 



=^-~l__^_ -_ _ ^ no means exempt from their 



attacks, as these fishes fre- 

 Ftg. 38.- SAW-FISH. quently ascend large rivers to 



a considerable distance. 



The genera of beaked rays constituting this family differ from all the pre- 

 ceding groups by the much greater development of their pectoral fins, which 

 extend forwards to join the head, the portion of the head 

 Family and body thus surrounded by fins being technically termed 



RhinobatidcK. the disc. In these and the other rays referred to below, the 

 dorsal fins are shifted backwards to the more or less whip- 

 like tail, and the gill-slits are placed inferiorly, as is generally the mouth. 

 The RhinobatidcR are specially distinguished from their kindred by the 

 moderate development of the pectoral fins, of which the portion furnished 

 with cartilaginous rays does not extend forwards to the beak ; and the long 

 tail, which is marked on the sides by a fold of skin, carries two large dorsal 

 fins. In addition to the typical genus Rhinobatis, which includes a consider- 

 able number of species from all the warmer oceans, the present family com- 

 prises the Australian Trigonorhina and the two species of Rhynchobatis, from 

 the hottest regions of the Indian Ocean. The last-named is remarkable for 

 the beautiful structure of its teeth, which form a compact pavement, with a 

 prominent ridge in the middle line of one jaw fitting into a corresponding 

 depression in that of the other, and also having undulations at the sides. 

 From six to eight feet is a common length for these rays. Like the skates 

 and rays of the following families, the members of these genera are some- 

 what sluggish fishes, living near the bottom in water of moderate depth, and 

 flapping lazily along when in movement by the aid of their huge pectoral fins, 

 the tail acting merely as a rudder. When at rest, the colour of the upper 

 surface of a ray's back is so like the sand or mud on which the creature rests 

 that it often requires a practised eye to detect its presence. The ridges of 

 tubercles found on the backs of some species probably increase the resem- 

 blance by simulating lines of small stones on the sand. The food of rays 

 consists of shell-fish and various crustaceans, whose hard shells are instan- 

 taneously ground up by the powerful mill-like jaws. In seizing their prey, 

 these fish throw themselves right above it, so as to be able readily to convey 

 it to the mouth, which is situated on the lower surface of the head some 

 considerable distance behind the muzzle. 



The second family of rays includes the genera Raia, Psammobatis, and 

 Platyrhina, in all of which the disc is very broad, with its rayed portion ex- 

 tending as far forwards as the muzzle, while the tail is 

 Family Raiidce. marked on each side by a fold. Yery generally the skin is 

 roughened by tubercles, which may terminate in spines. To 



