ELASMOBRANCHII BATOIDEI 



461 



represented by complete skeletons in the Lithographic Stone of 

 Bavaria, the Upper Cretaceous of Mount Lebanon, and the L T pper 

 Eocene of Monte Bolca. Trygonorhina occurs in the Eocene. 



Fam. 3. Raiidae (Skates or Kays). The endoskeletally 

 supported portions of the large pectoral fins extend along the 

 lateral margins of the trunk and head from the pelvic fins to 

 the snout, and are confluent therewith, forming the lateral por- 

 tions of a large rhombic disc. The tail is slender, and sharply 

 marked off from the trunk. Usually two small dorsal fins on 

 the tail. Caudal fin small or absent. No serrated spine on the 



FIG. 264. Raia tmirrayi, from Kerguelen Island. A, male ; B, female. 

 (From Giinther.) 



tail. Caudal electric organs are often present. Larger or 

 smaller denticles or spines are generally present on the skin. 

 Oviparous. Egg -cases four -horned, without tendrils. Four 

 genera and from thirty to forty species. Found in all temperate 

 seas, a few ranging into deep water. 



The great majority of the species belong to the genus Raia 

 (Fig. 264), which chiefly inhabits temperate seas, but is more 

 abundant in the northern than in the southern hemisphere, and 

 approaches nearer to the Arctic and Antarctic regions than any 

 other Batoidei. The colour of the upper surface of the body is 

 closely assimilated to that of the sandy or gravelly bottom on 



