434 



Second Suborder. EATOIDEI. 



Gill-openings ventral. In a few of the genera, 

 which we place first, the habit is still that of the 

 Sharks ; but the body is depressed ; and in the typical 

 genera the trunk, which is surrounded by the im- 

 mensely developed pectoral fins, forms a broad flat 

 disk, with a thin and slender tail. Spiracles always 

 present. Five pairs of gill-openings. No anal fin ; 

 dorsal fins, if present, on the tail. — Hays. 



Inhabitants of all the temperate and tropical seas ; some species 

 exclusively pelagic ; others entering fresh waters, or entirely limited 

 to rivers within the tropics. 



S)jno2)sis of the Families and Genera. 



Fam. 1. PRISTID^. 

 Snout much produced, with lateral teeth, saw-like. 



Saw without tentacles 1. rristis, p. 430. 



Fam. 2. RHINOBATID^. 



Trunk gradually passing iato the strong and long tail, which is 

 provided with two dorsal fins and a caudal. Pectorals not ex- 

 tending to the snout. 



The first dorsal opposite to tlie ventrals 2. Rhipichobatm, p. 440. 



Dorsal fins at a great distance behind the ventrals ; anterior nasal valves 



not confluent 3. Bhinohatus, p. 441. 



Anterior nasal valves confluent into a broad flap with free a margin, 



4. Trygonorliina, p. 447. 



Fam. 3. TORPEDINID^. 



Trunk a broad, smooth disk. Rayed dorsal and caudal fins 

 generally present. An electric organ. 



Two dorsal fins ; ventrals separate ; spiracles at a short distance behind 

 the eyes 5. Torpedo, p. 448. 



Two dorsal fins ; ventrals separate ; spiracles immediately behind the 

 eyes ; tail longer than the disk G. Narcinc, p. 452. 



Two dorsal fins. Tail extremely sn all and short. 



7. Hj/ptws, p. 453. 



Ventral fins united 8. Discopyge, p. 453. 



One dorsal fin only 9. Astrapc, p. 454. 



Dorsal fins absent 10. Temera, p. 455. 



