538 SHARKS AND RAYS. 



of the species is highly esteemed as food ; and its fins, 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 fins, 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^:. 



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. Giinther 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 has 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 



