TYPICAL GROUP. 
5 2 3 
Typical Genus. 
expanded; and the spiracle is always small and may be wanting. The front 
teeth, and very frequently also those on the sides of the jaws, are formed on the 
type of a laterally compressed cone with cutting edges, at the base of which two 
or more smaller cones may be developed; but in one existing and many extinct 
genera the hinder teeth have blunt crowns adapted for crushing. The two branches 
of the jaws do not run parallel to each other, in consequence of which the teeth 
form oblique rows, whereas in the rays they are set in straight longitudinal rows. 
From the other sharks the members of the present family may be distinguished 
by the absence of spines in both the dorsal fins, of which the first is situated above 
the interval between the pectoral and pelvic pairs; by the presence of a nictitating 
membrane to the eye; and by the teeth, when fully formed, being hollow, and 
usually pointed. The bony elements in the skin take the form of minute granules, 
thus constituting the well-known “ shagreen,” as the dried skin is termed. 
In all the members of the typical genus ( Carcharias ) 
the muzzle is produced forwards, and the inferiorly-placed mouth 
is crescentic and armed with large, flat, triangular, single-coned teeth, of 
which the upper ones differ considerably in form from those of the lower jaw. 
Spiracles are absent, and there is a pit at the root of the caudal fin, which has a 
distinct lower lobe. At the present day these sharks are represented by between 
thirty and forty species, of which the blue shark is one of the commonest and 
most widely distributed; while in a fossil state the genus is known from the 
Tertiary formations. The blue shark frequently attains a length of from 12 to 
15 feet, but some of the other species are stated to grow to as much as 25 feet. 
In common with the other larger members of the suborder, all these sharks are 
more abundant in tropical than in temperate seas; but the blue shark is by no 
means an uncommon visitor to British waters, more especially on the southern and 
western coasts of Ireland. Mr. J. T. Carrington writes that they more usually 
wander to the British coasts “ in warm weather, especially in autumn, but they 
have been seen in June, and even in the month of March. They are nocturnal in 
their more active habits, taking rest and sleep in the daytime, often on the surface 
of the water, with a portion of the dorsal fin and extremity of the tail exposed 
above in the air. So gentle are they in their movements that, unlike many other 
monsters of the deep, they do not disturb the luminous creatures, which at the 
same time will be lighting every wavelet with their phosphorescence. Blue 
sharks are not very particular as to what fish they take as food, though those 
which are gregarious in their habits, like mackerel, pilchards, and herring, are 
most commonly hunted by them. It is on record that big fish, such as congers 
and the larger dog-fish, were found in a dead specimen from Cornwall. Occasion¬ 
ally they become entangled in the drift-nets set by the pilchard-fishers, but these 
sharks will also take a bait. Great care is necessary in landing a hooked specimen, 
in case it gives a blow with its tail, which may result in serious consequences, such 
as broken limbs or ribs.” It is a somewhat remarkable fact that in places like 
Aden, where sharks of various kinds abound, the natives will swim arid dive 
fearlessly in the open sea, where a European would be almost instantly devoured 
by these monsters. The blue shark has the whole of the upper-parts slaty blue, 
and the under surface white. 
