66 
ROOM XI. 
Nat. Hist. 
genera, according to the form of the nostrils, the posi¬ 
tion of the fins, and the absence or presence of the 
aperture behind the eyes. Some, as the Cessations 
and Spine Sharks, have a large bony spine in the front 
of the dorsal fin. 
The Hammer-headed Shark ( Zygcena) is peculiar for 
the head being flattened, truncated in front, and extend¬ 
ed horizontally on the sides, so as to resemble a hammer. 
The Sea Angels ( Squatina ) have a depressed body, 
and the mouth placed at the end, and not beneath the 
muzzle. 
The Saw Fish (. Pristis ) have, with the long body of 
the sharks, the branchial opening below, and the muzzle 
produced into a long spike armed on the sides with 
implanted bony spines. This horn, whence they de¬ 
rive their name, is so powerful, that they do not fear to 
attack the largest cetaceous animals. 
The Rays ( Raiidce ) are known by their flattened 
bodies, by their large fleshy and expanded pectoral 
fins, united in front to the muzzle, and behind to the 
ventral fin and the spine. Their eggs have a brown 
coriaceous shell, of a quadrangular form, with the angles 
prolonged into points. The tail of some, as the Rhino- 
bates ( Rhinobatus ) and Rhinae ( Rhina ), is thick, like 
those of the sharks; in others, as the true Ray (Raia), it is 
slender, and often armed by small spines. In the Sting 
Ray (: Trygon ) it is very long and slender, and armed 
with a long bony spine, serrated on both its edges. 
The Sea Eagles (. Myliobates) have a long tail like 
the Sting Rays, but their pectoral fins are very broad, 
so that they in some measure resemble a bird of prey 
with its wings extended. 
The Cephalopterae ( Cephaloptera ) very much re¬ 
semble the Sea Eagles, but their head is truncated in 
front, and the anterior edge of the pectoral fin expanded 
like two horns. 
The Electric Ray ( Torpedo ) is peculiar for its fiddle¬ 
shaped body. The mouth of most of the Rays is armed 
with tubercular teeth placed in close quincunx order on 
the 
