50 



Memoirs of the Indian Museum. 



[Vol. II, 



Length from anterior border of anus to anterior border of 



disk 

 Length of tail 

 Maximum Avidth of disk 



, , thickness of disk 

 Distance between the eyes 



, , from eyes to anterior border of disk 

 Height of dorsal fin 

 Length of dorsal fin 



Owing to the strong muscles of the disk, it is liable to undergo great changes in 

 shape ; the two specimens I have examined exhibit this ver>' clearly. The degene- 

 racy of the pectoral fins causes the disk to terminate, when viewed from above, some 

 little distance in front of the anus. 



The mouth, as in Astrape, is to some extent protrusible, but cannot be thrust out 

 bodily as a tubular structure like that of Narcine. 



The number of the type ( "b ) in the Museum register is F. ^^^"^ . 



Family MYLIOBATID^. 



Head distinct from disk, with a prominent snout or a pair of processes on the front 



of the head supported by two groups of cartilaginous jointed rays (cephahc fins) ; 



skull rectangular and box-like. Teeth fiat, rectangular and pavement-like, large. 



Disk wide in proportion to its length. Tail long and thin, with a dorsal fin at its 



root, with or without a serrated spine. 



Taking into consideration the great differences between the skull and teeth of 

 the " Myhobatina " and the " Ceratopterina," I think it as well to follow Miiller 

 and Henle, and also Jordan {Guide to the Study of Fishes, vol. i, pp. 551, 559, 1905), 

 in regarding them as distinct famihes, although I have not adopted the American 

 name " Mobulidae " for the latter group. 



The Myliobatidse, if this view be accepted, consist of the genera Rhmoptera, 

 Myliohatis and Aetobatis, each of which is represented by at least two species in Indian 

 seas. Of Rhinoptera I have only seen the skeleton and teeth, and I do not, therefore, 

 propose to discuss its Indian representatives. Of Myliohatis and Aetobatis, however, 

 the ' ' Golden Crown ' ' has obtained large numbers of specimens, which have afforded 

 invaluable material for the elucidation of several doubtful points. The three genera 

 may be distinguished by the following characters: — 



I. Head provided with a pair of distinct rayed appendages (cephalic fins) on 



the ventral surface. Teeth tesselated, in five or more series, the central one 

 being the broadest and the others decreasing in breadth from within out- 

 wards . . . . . . . . . . . . Rhinoptera. 



II. Cephalic fins encased in muscle and skin to form a single more or less conical 



snout. 



