CARTILAGINOUS FISHES. 
501 
livers and brooks. In some of tbe English rivers they are frequently 
taken in the eel-pots, weighing two and three pounds. They frequent 
stony bottoms, where they find small animals on which they feed. In 
its larva state it was long considered to be a distinct species of Am- 
mocetta; it is now, however, ascertained that it only acquires its 
perfect form at the end of its second or third year. 
II. Selachia. 
The Selachians include a great number of cartilaginous fishes, vary- 
ing much in form, including the rays, dog-fish, skate, torpedo, hammer- 
fish, sharks, and saw-fish ; they have pectoral and ventral fins. On 
each side of the neck, on the lower surface, are five gill-openings, in 
form of a slit to each gill. Many of the species have two blow-holes 
in the upper part of the head. The order is divided into Baiadm and 
Squalidm. 
RAIADAE. 
Of the Iiaiad.-e there are several genera, and many species. In 
Cephaloptera the head is truncated, with large, lateral eyes. In 
Mijlidbates it is projecting, the pectoral fins extending like wings. 
In Trygon it is enclosed by the pectorals. In the Skate ( Raia ) the 
body is rhomboidal, tail without spine, but two small dorsals near the 
top. In the Torpedo the body is nearly round, the tail short and 
fleshy, with two dorsals and a caudal fin. 
The White Eay, Raia batis (Fig. 348), reminds us of the lozenge 
shape, the point of the muzzle forming the lower angle, the longest ray 
of each pectoral forming the lateral angles, while the s ummi t of the 
tail forms the last angle ; the whole surface seems flat, but a swelling is 
distinguishable towards the head, on the upper surface, which bears, 
as it were, the contour of the body, properly so called, namely, the 
three cavities of the head, the throat, and the belly, which occupy the 
centre of the lozenge, beyond which the pectoral fins extend. These 
fins, though covered with a thick skin, permit the cartilaginous rays, 
with their articulations, to be very distinctly seen. 
The head of the white ray, which terminates in a muzzle slightly 
Pointed, is attached behind to the cavity of the breast. The mouth, 
placed in the lower part of the head and far from the extremity of the 
Muzzle, is elongated ; its edges are cartilaginous, and furnished with 
