7S 
SKATES. 
The distinguishing marks of this family as compared with 
the Sharks, are a general depression and flatness of the body, 
with a large expansion of the pectoral and ventral fins; the 
former being united to and encompassing the head, so that 
together they form a disc, which is either rounded or of a 
rhorab-like form, with the angles slightly marked; a structure 
that displays a remarkable adaptation to the peculiar habits of 
this tribe. The snout in most of the species projects, and in 
all the mouth and nostrils are under the head, the latter 
being united to the former by a superficial channel, or deep 
fold in the skin. The gill openings are five in number, as 
in the Sharks, hut they are placed on the under surface; and 
on the head, not far behind the eyes, are the spiracles or 
temporal orifices, which, when they exist in the Sharks, are 
generally small, but in this family they are large and open, 
although capable of being closed at the will of the creature; 
and their use is more apparent in the present class; for as it 
is their habit to lie flat on the ground, it becomes necessary 
that they should be furnished with an apparatus sufficient to 
give passage to a full supply of water to the gills for the 
purpose of breathing; at a time when the mouth must for a 
long time remain shut, and the current from that direction 
consequently be interrupted, even if it ever exist. That this 
supply of water needs to be large and constantly repeated, 
may be judged from what Monro describes of the extensive 
capacity of the interior structure of the gills, the superficial 
extent of which he estimates as amounting to almost the whole 
external surface of the human body. Thus, says he, in each 
side of the body of a Skate there are four double gills, or 
gills with two sides each, and one single gill, on which the 
branchial artery (which brings the blood for purification) is 
spread out. On each of these sides there are about fifty 
