RAJIFORMES 



161 



If. 



.el. 



almost its extreme condition (Fig. 129, A). The slender tail is sharply 



marked off from the large ' disk.' Small dorsal fins are usually carried 



near its extremity, and the caudal is much reduced or absent. The tail is 



triangular in section, with 



paired longitudinal keels ; d nc 



some of its muscles are 



usually converted into an 



electric organ (Fig. 124) 



(Ewart[132]). Therhombic 



disk is formed chiefly by 



the huge pectoral fins, whose 



anterior axis and radials 



reach forward to the pre- 



orbital process and beyond. 



In Platyrhina they almost, 



and in Sympterygia they 



., , ,1 '^Ji vertebral centrum ; <?, dorsal denticle ; el, electric organ ; 



quite meet in the middle Lfj longitudinal fold ; m, my otome; H.C, nerve-chord. 

 line. The basihyal is a 



very slender transverse rod, and the basibranchials are fused to a simple 

 broad plate, perhaps including some hypobranchials. 



The pelvic girdle bears a pair of prepubic processes. In Cyclolatis 

 not only these but also the iliac processes are very long. The pelvic 

 fins are deeply notched, an anterior lobe being developed which is 

 supported by specially enlarged anterior radials (Fig. 89). The ribs 

 are very short. The teeth are small, blunt or pointed, and may differ in 

 the two sexes. The dorsal surface is frequently armed with very large 

 denticles, which may fuse into compound plates (Acanthobatis). 



Eelemnobatis, Tlnoll.jAsterodermus, Ag.; Jurassic, Europe. Acanthobatis, 

 Larr. ; Miocene, Europe. Oncobatis, Leidy ; Pliocene, N. America. Cyclo- 

 batis, Eg. ; Cretaceous, Syria. Raja, Cuv. ; temperate and tropical seas, 

 to Cretaceous in Syria, and Eocene in Europe. Platyrhina, M. and H. ; 

 Pacific, and to Eocene, Europe. Sympteryyia, M. and H. 



Fie. 1 _>-. 

 Transverse section of the tail of Raja duruta. c, 



GROUP B. TORPEDINOIDEI. 



The family Torpedinidae is perhaps an oft'shoot from Group A, 

 which it resembles in the structure of the pelvic girdle. It differs, 

 however, in the loss of the median rostral process and in the 

 development of anterior electric organs. The ceratotrichia are lost. 



Family TORPEDINIDAE. In general structure the electric rays 

 resemble the Rhinobatidae, but the tail is more distinctly marked off from 

 the disk. The caudal fin is usually little developed, and the body is 

 smooth. The disk is very rounded ; the median rostral cartilage has' 

 been lost in Torpedo, but in Narcine a considerable rostrum remains. 

 The edge of the disk is supported by the expanded pectorals, which do 

 not nearly meet in front, the wide intervening space being filled by 

 paired rostral processes, and the greatly enlarged preorbital cartilages 

 articulating in front of the nasal capsules (Fig. 125). In Torpedo, 



