88 MANUAL OF NATURAL HISTORY. 



perpendicular, hexagonal columns, the ends of which 

 are covered by the dorsal and ventral integuments. 

 Each separate column, when recent, seems like a 

 mass of clear trembling jelly ; but consists of a series 

 of delicate membranous plates, inclosed by a proper 

 capsule, and separated from each other by a small 

 quantity of limpid, albuminous fluid. Each half of 

 this electric battery derives its nervous influence 

 from one branch of the trigeminal, and four branches 

 of the vagus nerves. The battery is thus vertical, 

 and its plates horizontal, and the direction of the 

 current is from above downwards, the dorsal surface 

 being positive, and the ventral negative.* 



7. FAMILY. Beaked-Rays (Rhinobatidse). Muzzle 



generally beaked and pointed ; mouth undu- 

 lated ; teeth rounded or elliptical, in some 

 broader than long, and longer on summit of 

 undulations ; body smooth ; caudal fin bilo- 

 bular, or cut obliquely, forming one lobe. 



8. FAMILY. Saw-Fishes (Pristidae). Snout pro- 



duced into a long, flat, osseous, saw-shaped 

 blade, with teeth on the lateral edges ; body 

 flattened before, somewhat elongated pos- 

 teriorly ; skin with very small, flat, roundish, 

 or six-cornered scales ; mouth beneath. 



II. SU-OfiDfiIt.SiLAKKS (Squalinse). 



Body elongated ; tail fleshy, thick ; branchial 

 openings lateral ; skull without frontal cartilage. 



* See " Swainson's Natural History of Fishes," vol. i., p. 178 ; and 

 " Owen's Lectures on Comparative Anatomy," vol. ii., p. 212. 



