2898 SHARKS AND RAYS 



transverse section presents a star-like arrangement. All these fishes have an anal 

 fin, and the form of the body elongated and subcylindrical, while the tail is power- 

 ful and well adapted for swimming. In no case are the pectoral fins 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 

 18 produced forward, and the inferiorly-placed mouth is crescentic and 

 armed with large, flat, triangular, single-coned teeth, of which the upper ones dif- 

 fer 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 twelve to fifteen feet, but some of the other 

 species are stated to grow to as much as twenty-five feet. In common with the 

 other larger members of the suborder, all these sharks are more abundant in trop- 

 ical 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 por- 

 tion 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 dogfish, were found in a 

 dead specimen from Cornwall. Occasionally 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 



