.lATOlDET. 



435 



Fam. 4. RAJID^. 



Disk l)road, rhombic, generally rough ; tail with a longitudinal 

 fold on each side. Pectorals extending to the snout. No electric 

 organ. No serrated caudal spine. 



Caudal fin rudimentary or absent ; each ventral deeply notched^. 



11. Ititja, p. 455. 

 I'ectorals confluent in front of the snout ; each ventral deeply notched. 



12. Psammohatis, p. 470. 

 Caudal fin rudimentary ; pectorals confluent in front of the snout ; ven- 



trals Avithout notch 13. S;/mj^ten/f/ia, p. 470. 



Caudal fin well developed 14. Platyrhina, p. 470. 



Fam. 5. TRYGONID^. 



Pectoral fins uninterruptedly continued to and confluent at the 

 extremity of the snout. Tail without lateral longitudinal folds. 



* Tail without serrated spine. 



Tail long 15. Uroc/ymnus, p. 471. 



Tail short, with strong spinous excrescences round the basal portion. 



16. Elli2^esurus, p. 472. 



** Tail with a barbed spine. 



Tail long, finless, sometimes with a cutaneous fold below, which does noi 

 extend to its extremity 17. Trygon, p. 472. 



Tail with a rayless cutaneous fold below, which extends to its extremity. 



18. Tcenixira, p. 483. 



Tail with a distinct rayed terminal fin 19. Urolnphus, p. 485. 



Tail very short, without terminal fin ; body at least twice as broad as 

 long 20. Pteroplatea, p. 486. 



Fam. 6, MYLIOBATIDiE. 



Sides of the head free from the Bertnral fins ; snout with a de- 

 tached pair of cephalic fins. 



A. Teeth large, flat, tessellated Myliobatina. 



The cephalic fins form a soft appendage in front of the snout. Teeth in 

 several series, of which the middle contains very broad teeth. 



21. MyUobatis, p. 488. 



Only one series of very broad teeth 22. Aetohatis, p. 492. 



The cephalic tins separate, and forming a pair of lobes at the lower side of 

 the snout 23, Rhinoptei-a, p. 490. 



B. Teeth very small ; cephalic fins forminr/ a pair of separate appen- 



dages in front of the snout Ceratopterina. 



Teeth in both jaws 24. Dicerohatis, p. 49<). 



Teeth in the lower jaw only 25. Ctratoptera, 497. 



2 f2 



