SORTATION. 



21 



It contains but two genera. In one, Torpedo, the caudal is well 

 developed, and the side fins, let us call them the wings, are 



almost semi-circular ; in 

 the other, Raia, the tail 

 fin is rudimentary or 

 absent, and the wings 

 Fig. S.-BRANCHED RAY. are angular. Of Torpedo 



we have only two species 



T. marmorata, the marbled torpedo, which is mottled or 

 spotted, and T. nobiliana, the common torpedo, which is greyish, 

 with or without a few blotches, the two being probably varieties 

 of the same species coloured according to environment. These, 

 it need hardly be mentioned, are the electric rays that have given 

 their names to the submarine engines of destruction that in no 

 way resemble them. 



A genus of greater importance, though perhaps of less interest, 

 is Raia, which has ten representatives in British waters, divisible 

 into two groups, five in each, those in which the snout is short 

 and those in which it is long. Of the long-nosed rays, one only 

 has the under-surface brownish, that being R. batis, the skate that 

 is generally eaten, though several of the other species are equally 

 edible and are frequently sold as substitutes, the rays being the 

 chief constituents of the mysterious " roker " of the Billingsgate 

 Market report. The other four consist of 

 the long-nosed skate, R.oxyrliynchus, in which 

 the lower surface is grey ; the flapper skate, 

 R. tnacrorhynchus, in which it is white with 

 black spots; the white skate, R. alba, in 

 which it is pure white, there being no 

 row of spines round the eye, but a central 

 row of spines on the tail with a lateral row 

 on each side of it ; and, finally, the sha- 

 green ray, R. fullonica, in which the lower 

 side is also white, and there is a row of 

 spines round the eye but no middle row of spines on the tail. 

 Two of the short-snouted rays are brown underneath R. radiata, 

 the starry ray, in which the brown "is unspotted, and R. maculata> 

 in which it is spotted with black. Three are white underneath, 

 the most strikingly marked being the cuckoo-ray, R. circularis, in 

 which the under surface is generally edged with black and the 

 upper surface has a black and yellow patch on each side of the 



median line. The other two are both 

 spiny, the painted ray, R. microccllata, 

 having the spines confined to the median 

 line, and the thornback, JR. clavata, 

 having them all over the body ; and 

 the spines are unmistakable, as can 

 be seen by the sample (Fig. 4). 

 They are almost as remarkable as 

 the crushing-teeth, as shown in the 

 diagram of those in the male's upper 

 Fig. 5. UPPER JAW OF jaw (Fig. 5). 

 MALE THORNBACK. We have now to devote our atten- 



Fig. 4. SCALE OF 

 THORNBACK. 



