346 



FISHES. 



all tropical seas, and of exceedingly common occm-rence in 



^ the Atlantic and Indian Oceans ; it 



does not seem to grow to a very large 

 size (perhaps not exceeding 5 feet in 

 width), and is readily recognised by 

 numerous round bluish-white spots, 

 with which the back is ornamented. 

 Fossils of this genus occur in the 



Fig. i3i.-Aetobatis subai- English Eoccues and the Swiss Molasse. 



ciiatus, from Bracklesliam. _, „, , ,. 



Ehinoptera. — The cephalic appen- 

 dages are bent inwards, and situated at the lower side of the snout. 

 Nasal valves confluent into a broad flap, Avith free margin. Teeth 

 broad, flat, tessellated, in five or more series, the middle being the 

 broadest, and the others decreasing in width outwards. Tail 

 very slender, with a dorsal fin before the serrated spine. 



Seven species from tropical and sub-tropical seas are 

 known ; of Rhinoptera 

 polyodon nothing is known 

 except the jaws ; and 

 as its dentition is very 

 peculiar, no opportu- 

 nity should 1)6 lost of 

 obtaining and preserving 

 entire animals. Teeth 

 very similar to those of 

 existing species, and de- 

 scribed as Zygobatis, oc- 



Fig. 132. — Rhinoptera 

 woodwardi ; fossil. 



Lower Jaw. 

 Fig. 133. — Rhinoptera polyodon. 



