454 FISHES CHAP, 
the eastern and southern coasts of England. The Fish is 
gregarious in its habits, often swimming in shoals near the 
surface. The name “ Basking Shark” has been suggested by 
its habit of lying motionless on the surface in warm or calm 
weather, as if basking in the sun, with its dorsal fin protruding 
from the water. Unless attacked, this Shark is quiet and 
inoffensive. It derives its food-supply from small pelagic Fishes, 
and also from marine Invertebrates, which are strained from the 
water by the fringes of long, slender gill-rakers with which 
the branchial arches are provided. At one time harpooned 
and caught off the Irish, Scotch, and Norwegian coasts for the: 
sake of the oil obtained from its liver, the Fish is now of little 
economic importance. Nothing is known of its mode of repro- 
duction. 
Extinct species of Cetorhinus have been founded on detached 
vertebrae and isolated teeth from deposits of Pliocene age in 
Belgium and Italy, and possibly from still earlier Tertiary 
formations. Dermal spines similar to those found on the 
claspers of the males in the existing species occur in the Antwerp 
Crag, and in the Red Crag of Suffolk. 
Fam. 12. Rhinodontidae——Two dorsal fins, without spines, 
the anterior a little in front of the pelvic fins, the second opposite 
the anal. Tail with lateral keels and a pit at its root. Spiracles 
small. Nictitating membranes absent. Mouth and _ nostrils 
nearly terminal. Teeth very minute, numerous, and conical in 
shape. 
One genus, Rhinodon, with one or two species, is known. These 
Sharks are very widely distributed, specimens having been seen 
or captured in the neighbourhood of Ceylon, at the Seychelles, 
the Cape of Good Hope, Callao on the Peruvian coast, in the 
Gulf of California, and off the coast of Florida. Rhinodon is 
probably the largest known Shark. It is stated to exceed 50 
feet in length, but to be quite harmless. Scarcely anything is 
known of its habits, but the small size of the teeth, and the 
length of the gill-rakers, which resemble those of the Basking 
Shark, suggest a similar kind of food. 
Fam. 13. Spinacidae.—T'wo dorsal fins, the first in advance 
of the pelvic fins. Anal fin absent. Nictitating membrane 
absent. Spiracles rather large. Vertebrae cyclospondylic. Teeth 
variously modified in different genera. 
