10 Memoirs of the Indian Museum. [Vol. II, 



characters, which are discussed bejow. I cannot regard it as genericalty distinct from 

 its alHes usually placed in Rhinohatus. 



The two Indian genera recognized in this paper are, therefore, Rhamphohatis , 

 Gill (1861), and Rhinohatis, Bloch and Schneider (1801). 



Genus Rhamphobatis, Gill. 



Head rounded in front, not produced into a rostrum. Back bearing large compressed 



bony tubercles arranged in rows. Teeth lozenge-shaped, transverse, with many 



sinuous, parallel transverse ridges. 



I have made a careful comparison between the skull of the one species of this 

 genus and that of Rhinobatis djeddensis. The cranial cartilages are somewhat different 

 in the two species. In the latter a single rostral cartilage projects forward between the 

 nasal capsules ; its ventral surface is hard, solid and undivided, but there is a broad 

 and lengthy longitudinal depression on the dorsal surface. In Rhamphcbatis , on the 

 other hand, a pair of rostral cartilages, which are much broader and flatter than the 

 single one in Rhinohatis and only joined to one another at the base by membrane, 

 arise in the same position and only unite as cartilages near the tip of the snout. The 

 condition in Rhinohatis gramilatus, R. scklegelii and R. halavi is exactly the same as 

 in R. djeddensis. 



There is, moreover, a distinct difference between the teeth of Rhamphohatis and 

 those of all the species of Rhinohatis I have examined. In the latter genus, although 

 the teeth differ considerably in the different species, they may be described in all cases 

 as having a single transverse ridge, which sometimes is raised in the centre so as to 

 be almost conical. In Rhamphohatis , on the other hand, the teeth bear numerous 

 wavy transverse ridges , none of which is much better developed than the others. 



Rhamphohatis ancylostomus (Bloch and Schneider). (PL v, fig. 5.) 



Pectoral fins with the anterior margins not joined by skin to the sides of the head. A 

 median dorsal ridge of large, compressed, irregular tubercles running from just 

 behind the spiracles a httle more than half way to the first dorsal fin ; a similar 

 ridge on either side running along the internal margin of the orbit and spiracle and 

 continued in a somewhat less conspicuous fashion round the anterior margin of the 

 former; a patch of similar tubercles in front of each of these lateral ridges, which 

 are continued posteriorly, after a considerable interruption, by .short and feeble 

 ridges in a straight line with them ; a still shorter and feebler outer lateral ridge 

 on either side parallel to the main one. The two dorsals and the caudal fin 

 about equidistant from one another ; the posterior rather smaller than the an- 

 terior ; the lower lobe of the caudal long and pointed. A strong ridge on the 

 side of the tail. Mouth strongly undulated, the two downward projections on 

 the upper jaw and the three upward projections on the lower jaw approximately 

 equal; the teeth lozenge-shaped, the breadth f— i^ of the length; ten distinct 

 ridges on the unworn teeth; teeth much smaller on the excavations of the jaw, 

 than on the projections. 



