Rays do not descend to the same depth as Sharks; with one exception,[37] at least, none have been known to have been caught by a dredge worked in more than 100 fathoms. The majority are coast fishes, and have a comparatively limited geographical range, none extending from the northern temperate zone into the southern. However, some, if not all the species of the family _Myliobatidæ_, which includes the giants of this division of Plagiostomes, have a claim of being included among the Pelagic fishes, as they are frequently met with in the open ocean at a great distance from the shore. It is probable that the occurrence of such individuals in the open sea indicates the neighbourhood of some bank or other comparatively shallow locality. Many species are exclusively confined to fresh water, and occur far inland, especially in tropical America. The majority are oviparous. All have five pairs of gill-openings. The number of known species is about the same as that of Sharks, viz. 140. FIRST FAMILY--PRISTIDÆ. _The snout is produced into an exceedingly long flat lamina, armed with a series of strong teeth along each edge_ (saw). PRISTIS.--Body depressed and elongate, gradually passing into the strong and muscular tail. Pectoral fins, with the front margins quite free, not extending to the head. No tentacles below the saw. Teeth in the jaws minute, obtuse. Dorsal fins without spine, the first opposite or close to the base of the ventrals. “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._