344 FISHES. 



Pteroplatea. — Bodyat least twice as broad as long; tail very- 

 short and thin, without or with a rudimentary fin, and with a 

 serrated spine. Teeth very small, uni- or tri-cuspid. 



Six species from temperate and tropical seas. 



Sixth Family — MTLioBATiDJi;. 



The disk is very hroad, in consequence of the great develop- 

 ment of the pectoral fins, which, however, leave the sides of the 

 head free, and reappear at the extremity of the snout as a 

 pair of detached (cephalic) fins. Viviparous. 



" Devil-fishes," " Sea-devils," or " Eagle-rays." Generally 

 of large size, inhabiting temperate and tropical seas. Some 

 genera possess a pair of singular cephalic processes, which 

 generally project in a direction parallel to the longitudinal axis 

 of the body, but are said to be flexible in the living fish, and 

 used for scooping food from the bottom and conveying it to the 

 mouth. In all the species the dentition consists of perfectly 

 flat molars, forming a kind of mosaic pavement in both the 

 upper and lower jaws : a most perfect mechanical arrange- 

 ment for crushing alimentary substances. 



Myliobatis. — Teeth sexangular, large, flat, tessellated, those 

 in the middle much broader than long ; several narrower series on 



Fig. 129. — Jaws of an Eagle-Eay, Myliobatis aquila. 



