RAYS. 



343 



Urogymnus. — Tail long, without fin or spine, sometimes with 

 a narrow cutaneous fold below. Body densely covered with 

 osseous tubercles. Teeth flattened. 



Only one species is known {U. asperrimus), common in 

 the Indian Ocean, and with a body from 4 to 5 feet long ; 

 the skin is frequently used for covering shields and the handles 

 of swords and other weapons, its rough surface offering a 

 firm hold to the hand. 



Trygon. — Tail very long, tapering, armed with a long arrow- 

 shaped barbed spine. Body smooth or with tubercles. Nasal 

 valves coalescent into a quadrangular flap. Teeth flattened. 



Some twenty-five species are knowm, one of which (T. 

 pastinaca) extends from the south coast of England and the 

 east coast of North America through the Atlantic and Indian 

 Ocean to Japan. The majority of the species belong to the 

 tropical parts of the Indian and Atlantic Oceans; some 

 inhabit exclusively fresh- waters of eastern tropical America. 

 A closely allied genus is Tceniura, with six species. 



IJROLOPHtrs.-^Tail of moderate length, with a distinct rayed 



Fig. 128. — Urolophus cruciatus, from Australia. 



terminal fin, armed with a barbed spine, without or with a 

 rudimentary dorsal fin. Teeth flattened. 



Seven species from tropical seas, apparently of small size. 



