538 
SHARKS AND KAYS. 
of the species is highly esteemed as food; and its tins, like those of sharks, are, 
after due preparation, exported to China. 
Fossil remains of extinct species of the genus occur throughout a large portion 
of the Tertiary formations; and an allied Eocene genus, Propristis, differs by the 
circumstance that the teeth of the saw are not implanted in calcified sockets. A 
very remarkable type of saw-fish ( Sclerorhynchus ) has left its remains in the 
Cretaceous rocks of Syria. Not only does this fish differ from the living forms by 
the distinctly depressed form of the relatively short and broad body, and the 
backward extension of the pectoral tins, which almost reach the pelvic pair, but 
the teeth, instead of being implanted in sockets, are merely attached to the skin by 
an expanded and crimped base. Moreover, the central of the three rods in the 
interior of the saw extends to the saw’s extremity, instead of stopping short; 
and it is not a little interesting to find that from the smaller teeth at the base of 
the saw a complete gradation can be traced to the tubercles dotting the skin. 
Assuming, as is most probably the case, that saw-fishes are nothing more than 
highly specialised sharks, it is somewhat remarkable to find that the earliest known 
member of the family has a somewhat skate-like form of body, and a type of 
dentition which could not apparently be very readily modified into that of the 
existing forms. 
The Beaked Rays,— Family Rhinobatid^e. 
With this family we come to the first of what may properly be termed the 
rays and skates, in all of which the pectoral fins are so extended forwards as to 
join the head, and thus form, with the body, the so-called “disc”; the dorsal fins 
being always situated on the tail, and the mouth being generally, and the gill-clefts 
always, inferior. In the present family the tail is long and powerful, with two 
well-developed dorsal fins, and a longitudinal fold on each side; the disc is not 
excessively dilated, the rayed portion of the pectoral fins stopping short of the 
beak; and there is no electric organ. Skates and rays in general are among the 
most hideous and repulsive of all fish, some of them—especially in the warmer 
seas—attaining enormous dimensions; while some are dangerous from the wounds 
inflicted by the spines of their tails. The tooth - like tubercles on the skin 
frequently attain a great development, and are aggregated into prominent bosses 
or longitudinal ridges. Dr. Gunther writes that the mode of life of these fishes is 
quite in accordance with the form of their body, the true rays leading a sedentary 
life, moving slowly on the bottom of the sea, and rarely ascending to the surface. 
Their tail ha's almost entirely lost the function of an organ of locomotion, acting in 
some merely as a rudder. They progress slowly by means of the pectoral fins, the 
broad and thin margins of which are set in an undulating motion, entirely identical 
with that of the dorsal and anal fins of the Pleuronectidce. Like the sharks, they 
are exclusively carnivorous, but being unable to pursue and catch rapidly moving 
animals, they feed chiefly on molluscs and crustaceans. The colour of their integu¬ 
ments assimilates, however, so closely to that of their surroundings, that other fishes 
approach near enough to be captured by them. The mouth of the rays being 
entirely on the lower surface of the head, the prey is not directly seized by the 
