MANUAL OF NATURAL HISTORY 87 



2. Family. — Eagle-Rays (Myliobatid^e). Head par- 



tially disengaged from pectorals ; mouth 

 transverse ; teeth large, mosaic-like ; eyelids 

 wanting ; tail long, with a back-fin on root, 

 and a serrated sting behind. 



3. Family. — Sting-Rays (Trygonidee). Head la- 



terally enclosed by pectorals ; teeth trans- 

 versely elliptical ; tail without any fin, or 

 merely a low, vertical, cuticular hem, and 

 with one or more sharp serrated spines. 



4. Family. — Stingless-Rays (Anacanthidse). Teeth 



flat, transversely elliptical ; tail without any 

 fin, or with a small one on under side ; no 

 spine. 



5. Family. — Skates (Raiidse). Body rhomboidal ; 



tail depressed, slender, generally with a low 

 terminal fin, and frequently with rows of 

 small spines ; skin smooth, or with small 

 curved prickles ; teeth flat, pavement-like, 

 and pointed in males in spawning time. 



6. Family. — Torpeclos (Torpedinidse). Head very 



large and surrounded by pectorals, so as to 

 form a circular disk ; tail short, fleshy, de- 

 pressed at base, cylindrical at extremity ; 

 mouth beneath ; teeth pointed or flat. 

 Some members of this family are remarkable for 

 their power of communicating at will powerful elec- 

 tric shocks. The organs whence these proceed are 

 two in number, lodged on either side of the head, 

 and encompassed by the gills, and the anterior bor- 

 ders of the pectoral fins. They consist of a mass of 



