“Saw-fishes.” Abundant in tropical, less so in sub-tropical seas. They attain to a considerable size, specimens with a saw 6 feet long and 1 foot broad at the base not being of uncommon occurrence. The saw, which is their weapon of attack, renders them most dangerous to almost all the other large inhabitants of the ocean. Its endoskeleton consists of three, sometimes five, rarely four, hollow cylindrical tubes, placed side by side, tapering towards the end, and incrusted with an osseous deposit. These tubes are the rostral processes of the cranial cartilage, and exist in all Rays, though in them they are shorter and much less developed. The teeth of the saw are implanted in deep sockets of the hardened integument. The teeth proper, with which the jaws are armed, are much too small for inflicting wounds or seizing other animals. Saw-fishes use this weapon in tearing pieces of flesh off an animal’s body or ripping open its abdomen. The detached fragments or protruding soft parts are then seized by them and swallowed. Five distinct species of Saw-fishes are known.
Saws of extinct species have been found in the London clay of Sheppey and in the Bagshot sands.
Second Family—Rhinobatidæ.
Tail strong and long, with two well-developed dorsal fins, and a longitudinal fold on each side; caudal developed. Disk not excessively dilated, the rayed portion of the pectoral fins not being continued to the snout.
Rhynchobatus.—Dorsal fins without spine, the first opposite to the ventrals. Caudal fin with the lower lobe well developed. Teeth obtuse, granular, the dental surfaces of the jaws being undulated.
Fig. 125.—Dentition of Rhynchobatus.
Two species, Rh. ancylostomus and Rh. djeddensis, are very common on the tropical coasts of the Indian Ocean. They feed on hard-shelled animals, and attain scarcely a length of 8 feet.
Rhinobatus.—Cranial cartilage produced into a long rostral process, the space between the process and pectoral fin being filled by a membrane. Teeth obtuse, with an indistinct transverse ridge. Dorsal fins without spine, both at a great distance behind the ventral fins. Caudal fin without lower lobe.
Numerous on the coasts of tropical and sub-tropical seas; about twelve species. Trygonorhina is an allied genus from South Australia.