86 
RAIA. 
SKATES AND BAYS. 
The disc approaching to the figure of a rhomb; the tail slender, 
and furnished near its termination with two rounded dorsal fins; the 
jaws crowded with teeth. 
SKATES. 
When the number of species in a recognised genus is considerable, 
it has been found convenient to divide them into groups, according to 
some distinguishing marks, w'hich are perhaps of less importance than 
can be regarded as necessary to constitute a generic distinction, and yet 
in which a certain number of those marks come together with the 
absence of others. This has in fact been a leading principle in the 
arrangements made by some eminent naturalists, and it is according 
to it that I would make a separation in the Cuvierian genus Raia, 
by which the Skates, properly so called, will be kept di.sliuct from 
those which are in common language more properly called Rays. 
Among fishermen they are for the most part so distinguished on 
account of the greater size, but the fact of magnitude would be 
attended by too much uncertainty to be a proper mark of distinction, 
and it is on other accounts unnatural. A better, because a more 
decided and permanent mark is the colour of the under part of the 
body, which in the proper Skates is dusky, arising from a large 
number of ducts and pores, that appear through the skin in lines, 
and cause it to appear of a dark grey tint. Their use is to pour 
out mucus or slime, which renders the surface of the body soft and 
slippery, and tends no doubt to their safety and comfort. In the 
proper Rays pores of a like kind also exist, and the slime poured 
out is abundant; in which they differ from their congeners the Sharks, 
for in them the pores are not rendered visible by their colour, and 
the colour of their under surface is in consequence pure white. 1 
therefore distinguish the former division, which comprises the Skates, 
as a genus, under the ancient name of Batis; and which will be 
sufiiciently distinguished by joining to the characters of Raia, already 
given, the addition, that the under surface is covered with dusky 
lines and spots. 
