ORDER ELASMOBRANCHEI. 



933 



Family Rhinobatid^e — With this family we come to Fishes to 

 which the general term Rays may be applied ; all of them are 

 characterised by their extremely depressed bodies and the great de- 

 velopment of the pectoral fins, so that the body proper with its fins 

 is termed the "disk." The teeth always form a kind of pavement 

 (figs. 856, 857). In the present family the tail is long and stout, 

 with two well-developed dorsal fins ; while there is also a caudal fin, 

 with a longitudinal fold on either side. The disk is not excessively 

 developed ; the rayed portion of the pectoral fins not extending to 

 the snout. The type-genus Rhinobatis (Sfiathobatis) is represented 

 at the present day by about a dozen species, which inhabit the 

 warmer seas, and attain huge dimensions. The snout is produced 

 into a long rostrum, which is connected with the pectoral fin by a 

 membranous expansion (fig. 854). The teeth are obtuse; and the 

 dorsal fins are devoid of spines. In time this genus ranges from 

 the Kimeridgian to the present day ; species being recorded from 

 the lithographic limestones of Bavaria (fig. 854) and France; from 

 the Portlandian of France ; the Chalk of the Lebanon and Italy ; 

 the Middle Eocene of Monte Bolca ; the Miocene of Wurtemberg ; 

 and other localities. The Austral- 

 ian Trygonorhina, which differs in 

 the structure of the nasal valves, 

 is said to occur in the Middle 

 Eocene of Italy. Finally, the gen- 

 era Belemnobatis and Asterodermus, 

 respectively from the Kimeridgian 

 of France and Bavaria, appear to 

 connect the present with the fol- 

 lowing family. 



Family Raiid^e. — In the true 

 Rays or Skates (fig. 855) the 

 disk is broad and rhomboidal, 

 and usually has dermal rugosities ; 

 while the rayed portions of the 

 pectoral fins extend to the com- 

 paratively short snout. The tail 

 is also shorter than in the Rhino- 

 batidtz, with a longitudinal fold ; 

 and the development of the median 

 fin is subject to considerable varia- 

 tion. The type genus Rata (Actinobatis) has the tail very distinct 

 from the body (fig. 855); the pectoral fins not reaching to the 

 extremity of the snout ; two dorsals, and either a rudimental or no 

 caudal fin. The dentition (figs. 856, 857) often varies greatly in the 

 two sexes ; some or all of the teeth in the male being sharp, while 



Fig. 855. — The Burton Skate {Rain mar- 

 ginata), one -sixth natural size. Recent. 

 Britain. (After Gosse.) 



