THORNBACK RAY. 101 



sometimes the skin is covered with evident roughness; a circum- 

 stance which has led some observers to suppose such examples 

 to constitute separate species. I have also met with some 

 singular varieties, and of an opposite kind, which require notice 

 in this place. A male example, taken in comparison with 

 another of the same species, agreed with it in every particular, 

 except that its skin was altogether smooth, except a few rough 

 grains on the point of the snout, and the usual spines over 

 the eyes and on the border of the disk at the pectoral fins. 

 The usual roughness of the skin was altogether absent, and not 

 a single hooked spine existed otherwise on the body. The 

 colour was pale dusky brown, and not mottled, as is constantly 

 the case in ordinary examples; but having some fine longitudinal 

 lines. The liver was remarkably small, and black as if it had 

 been soaked in ink. 



In another example, which in form also closely resembled the 

 common Thornback Ray, no hook or spine could be discovered, 

 except a row that passed from the head along the back and 

 down the middle of the tail; with none behind the eyes or on 

 the sides of the tail. Surface of the disk very rough, more 

 so than in the common examples of this Ray ; the teeth flat as 

 in that fish, and in the centre of each tooth was a depression, 

 which was softer than at the border; so that each separate 

 tooth resembled a wide ring. The surface of the disk was an 

 intense black, but near the head bordered with a lighter colour; 

 and over the surface were scattered a few round spots of a 

 still darker colour. 



I have not thought it necessary to regard these examples as 

 forming distinct species ; principally because there are none 

 described by other observers to which they can be referred; 

 the It. rubus of Linnams and other authors appearing to me to 

 be a very uncertain species; and the resemblance of form was 

 in all respects, except the particulars here given, like that of 

 the Thornback Ray. 



