40 The Cartilaginoiis Fishes of Lower Bengal. [No. 1, 



formidable weapon. Habitat of the species unknown, but probably 

 tlie Lidian Ocean. 



The ordinary Trygons are of a more rhomboidal shape, witli close- 

 set flattened tubercles on the dorsal surface, occupying its medial 

 third only or less (according to the species), and the lateral border 

 of this tuberculated space is abruptly defined in adults. They have 

 generally one or more large globular bony tubercles in the centre of 

 the dorsal surface. 



Some have two spines on a comparatively sbort tail, as — 



17. Tr. imbricatus, (Bloeh), to which I doubt if Russell's fig. 

 IY correctly applies, and upon this is founded Pastinaca dorsalis, 

 Swainson. Russell's figure more probably represents the Tr. 

 immtjnis, Raines (Zool. App. to Life of Sir S. Raines) ;* and other 

 double-spined species (also with comparatively short tail) exist in 

 the Tr. iymna figured by Rüppell, and Tr. akojtj and Tr. ktjhlii 

 figured by Müller and Henle. As Buchanan Hamilton approximates 

 his Raia fluviatilis to R. Iymna, though referring merely to " the 

 spine on its tail," I think it likely that the present species is intended 

 by him, especially as it is so very abundant. They are not unfre- 

 quently brought to the bazar with one spine only torn away by the 

 fishermen ; but this small species is commonly brought with both 

 caudal spines complete. The males are larger than the females, and 

 have proportionally longer tail ; and very commonly the second 

 caudal spine of the female more especially does not extend beyond 

 the first one. I have not seen the male larger than 7f in. to base 

 of tail, the tail 13 in., and caudal spines 2| in. Some have a small 

 lanceolated tubercle on centre of dorsal surface, others two or more 

 even to a series of five or six along the median line. This species is 

 so very often brought in pairs to the bazar, a male and a female, that 

 I cannot help suspecting that it lives in pairs, the two being com- 

 monly taken together. 



Another type has an equally short tail, armed with one spine only, 

 and no dorsal tubercles whatever. To this appertains — 



18. Tr. walga, M. and H. : probably Tr. sindraki, Cuv., and 



* " Tr. corpore subquadrato, omnino Isevi, cauda longiore, spinis duabis serra- 

 tis citra médium armatá." 



