52 



Memoirs of the Indian Museum. 



[Vol. II, 



definite ridge running along the upper limit of each orbit and produced in front into a 

 short, horn-like structure measuring in adult specimens from 2 — 4 mm. in length. I 

 cannot detect any other peculiarity that seems to be correlated with the presence 

 of this horn, and Capt. Lloyd tells me that horned and hornless individuals are taken 

 together in the same haul of the trawl. I therefore propose to name the horned form 

 Myliohatis nieuhofii, var. cornifera, var. nov. (PI. ii, fig. 4.) 



The presence or absence of horns has been considered a specific character in other 

 species of the genus, but Jordan and Snyder^ suggest that these structures are decidu- 

 ous in a Japanese species (M. tohijei) . This is not the case as regards the Indian species. 

 In an embryo in the collection of the Indian Museum which measures 115 mm. across 

 the disk, the horns are already apparent, but they are absent from several other em- 

 bryos of about the same size ; unfortunately I have not been able to obtain a gravid 

 female of the variety cornifera . In some half-grown and old specimens they are absent , 

 in others present. In some horned individuals the denticles on the back are rather 

 more strongly developed than is usually the case in the typical form. 



The hornless form is much commoner than the horned one, but the latter is not 

 rare. Both have been taken in large numbers off the coasts of Orissa, Chittagong 

 and Burma, and less abundantly off the mouth of the Ganges. Apparently the species 

 prefers a rocky bottom, on which it is possible that it finds more food in the way of 

 molluscs. Its diet is not confined to molluscs, however, as both fish and prawns have 

 been found in its stomach. These are swallowed whole and are not crushed by the 

 teeth. 



The following measurements are interesting as illustrating the variation that 

 occurs as regards the teeth in this species :— 



No. 



Breadth of teeth of upper 

 jaw. 



Number of small teeth. 



Measurements of central tooth. 





Left. 



Right. 



Breadth. Length. 



I 



20 -o mm. 



3 



3 



13-5 mm. 



2 "25 mm. 



2 



i(ro ,. 



3 



3 



ii-o ,, 



2-25 ,. 



3 



I9'.5 -- 



3 



3 



12-0 ,, 



175 >, 



4 



17-0 ,, 



3-4 



2-3 



ii-o ,, 



1-5 „ 



5* 



i6-5 „ 



2 



3 



12-0 ,, 



2-25 ,, 



6 



12-0 ,, 



3 



3 



7-5 ,• 



1-25 „ 



7 



23-0 ,, 



3 



2 



ii-o ,, 



3-0 ,, 



8 



i7"o ,, 



3 



3 



IO-5 ,, 



I-Q ., 



9 



14-0 ,, 



3 



3 



10-5 ,, 



2-25 ,, 



ro 



27-0 „ 



3 



3 



2O*0 ,, 



2*25 ,, 



Proc. U. S. Nat. Mus., xxiii, p. 338 (igoo). 



