318 
CA RTIL AGINEI. — RAIAD^. 
We select the latter species for illustration. 
It is abundantly common all round the British 
coasts, as well as on those of western and southern 
THORNBACK. 
Europe. It attains a diameter of two feet; is 
brown above with paler spots, and white beneath. 
The whole upper surface is rough with minute 
points, and is studded with an irregular number 
of large hooked spines. The structure of these 
is peculiar ; each consists of an oval, rather thick 
disk of white bone, the centre of which rises 
into a sharp conical point curved backwards, the 
whole possessing a slight resemblance to one of 
the prickles on the stem of a rose-bush. A 
group of small ones of similar form surround 
each eye, and a row runs down the middle of 
the back in close series. The others are much 
larger, and irregularly scattered both over the 
body and the tail. 
The Thornback is much eaten by the poorer 
