312 
CARTILAGINEI. — RAIAD^. 
of the Sharks : the dorsals are two, sometimes 
three in number, small, and placed very far back 
upon the slender tail ; sometimes, indeed, close to 
its extremity ; a minute caudal is occasionally 
seen, but more frequently wanting ; the dorsals 
also are, in some species, obliterated. 
The eyes, and the temporal spiracles, are 
placed on the upper surface : the latter are much 
larger than in the Sharks, often exceeding the 
size of the eyes ; they communicate internally 
with the mouth and gills. The mouth, the 
nostrils, and the gill-openings are placed on the 
under-surface, and quite concealed from view in 
the ordinary position of the fish as it flounders 
along on the bottom of the sea. The gill-open- 
ings agree with those of the Sharks in number, 
form, and structure. The mouth is small, and 
set with numerous teeth, which are arranged in 
close array like paving- stones ; they are more or 
less square, and flat; but in old males, the 
middle ones assume a pointed form, overlapping 
one another, and pointing backward towards the 
throat. 
As in many of the Sharks, the eyes are fur- 
nished with a nictitating membrane^ or skin, which 
can be drawn over the eye-ball at pleasure, 
serving the purpose of an eyelid. 
The young of the Rays are enveloped at birth, 
like those of some of the Sharks, in capsules of 
thin horn or leathery substance. They are gene- 
rally more square in form, with the angles pro- 
duced, but not attenuated to long filaments. 
The accompanying figure represents the egg- 
capsule of the Common Skate, frequently found 
on our sea-beaches, and commonly called Skate- 
