40 FISH GALLERY. 



Raii (Saw-fishes and Rays). 



Wall- T ne suborder Raii or Batoidei includes the Saw-fishes, Skates, 



' and Rays. The form of the body is adapted for living on the sea- 

 bottom ; the pectoral fins are enlarged, and their front edges 

 encroach round the sides of the head ; the tail and median fins are 

 reduced, although these characters are less pronounced in the first 

 two families — the Pristidse and Rhinobatidse — than in those that 

 follow. In the more highly specialised forms the trunk, surrounded 

 by the immensely developed pectoral fins, forms a broad, flat disc, 

 of which the tail appears as a slender appendage (see Sting Rays, 

 Wall-case 4). The cartilaginous rays of the fins are greatly 

 developed and the dermal fin-rays reduced or absent. The eyes 

 and spiracles are on the upper surface of the body, and the five 

 pairs of gill openings on the under surface (see Raia, 112). The 

 upper surface is pigmented, the lower pale. The Rays lead a 

 sedentary life at the bottom of the sea and subsist on molluscs, 

 crustaceans, and small fishes ; they keep fairly near the coast, only 

 the Eagle Rays being found in the open ocean. Some species 

 occur in fresh water. In the more highly specialised forms 

 progression is effected by the gentle undulation of the long margin 

 of the pectoral fin, and not by a flapping of the whole fin, nor by 

 the lashing of the tail. The mouth opening is ventral, and very 

 slightly if at all curved, and the jaws are correspondingly straight 

 and transverse. The jaws are rounded in section, and several rows 

 of teeth are in use at the same time (see jaws 103 and 116). In 

 the highly specialised Eagle Rays the teeth are flattened plates 

 adapted for crushing (see jaws 1.22 and 126). 



The Pristidse, or Saw-fishes, are distinguished by the remarkable 

 prolongation of the rostrum of the skull, with its double ' saw ' of 

 lateral teeth (see tig. 21). In other respects the Pristidse may be 

 regarded as the least modified of the Batoidei or Raii ; they swim 

 freely, and have a body which is long, slightly depressed, and 

 passing gradually into the strong and muscular tail. Although 

 the pectoral fins have grown forward so far as to turn the gill- 

 clefts on to the ventral surface of the body they are not very 

 greatly enlarged. The dorsal fins have no spines ; the first is 



fishes 



