RAJIFORMES 1 59 



Except in the first two families, the nostrils are confluent with 

 the mouth, there being a well-marked fronto-nasal process. 



Although the main trend of the evolution of this Division has 

 been towards adaptation to a bottom-living habit, yet divergencies 

 can be traced amongst the various families. Accordingly, we divide 

 it into three groups (Jaekel [238]). In Group A, Rhinoraji, are 

 developed a large median rostral cartilaginous process, and a pelvic 

 girdle with paired prepubic processes. Group C has no cartilaginous 

 rostrum, and a median prepubic process. Group B, containing the 

 Tropedinidae, is perhaps an offshoot from Group A, having the same 

 type of pelvic girdle, but losing the rostrum almost completely. 

 It is, however, quite possible that the more shark-like Pristidae 

 and Rhinobatidae represent a primitive group from which the 



n 



Pig. 122. 



RhyncTiobatus djeddensis, Forsk. Dorsal view, and ventral view of the head. (After Day, 

 Fishes of India.) 



Rajidae, the Torpedinidae, and the Centrobatoidei have arisen as 

 three diverging branches. 



Group A. Rhinoraji. 



The rostrum is supported by a large median cartilaginous 

 process of the skull (Fig. 120). The tail becomes slender and the 

 dorsal fins shift back towards its tip. Two longitudinal keels 

 develop along its sides. Paired prepubic processes are present on 

 the pelvic girdle (Fig. 121). 



Family Rhinobatidae. The head and trunk are much depressed, 

 forming a ' disk ' produced forwards into a large rostrum ; the very large 

 pectorals do not yet reach the snout (Fig. 122). Their endoskeletal radials 

 attain neither the rostrum nor the large preorbital processes in the Jurassic 

 species. The tail is relatively small, is losing its heterocercal shape 

 by the reduction of the ventral lobe, but still blends in front with the 

 trunk. The blunt teeth are closely set on the jaws, and may form an 



