The rostral cartilage is produced, into an exceedingly long, flat lamina, armed along each edge with a series of teeth (saw).
These Sharks resemble so much the common Saw-fishes as to be easily confounded with them, but their gill-openings are lateral, and not inferior. They are also much smaller in size, and a pair of long tentacles are inserted at the lower side of the saw. The four species known (Pristiophorus) occur in the Australian and Japanese seas.
Squaloraja, from the Lias, is supposed to have its nearest affinities to this family.
B. Batoidei—Rays.
In the typical Rays the body is excessively depressed, and forms, with the expanded pectoral fins, a circular or sub-rhomboidal disk, of which the slender tail appears as a more or less long appendage. In the two families which we shall place first (Pristidæ and Rhinobatidæ), the general habit of the body still resembles that of the Sharks, but the gill-openings are ventral, as in the true Rays; the anal fin is invariably absent, and the dorsal fins, if developed, are placed on the tail. The mode of life of those fishes is quite in accordance with the form of their body. Whilst the species with a shark-like body and muscular tail swim freely through the water, and are capable of executing rapid and sustained motions, the true Rays lead a sedentary life, moving slowly on the bottom, 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 solely 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 Pleuronectidæ. They are exclusively carnivorous, like the Sharks, but unable to pursue and catch rapidly-moving animals; therefore they feed chiefly on molluscous and crustaceous animals. However, the colour of their integuments assimilates so closely that of their surroundings, that other fishes approach them near enough to be captured by them. The mouth of Rays being entirely at the lower surface of the head, the prey is not directly seized with the jaws; but the fish darts over its victim so as to cover and hold it down with its body, when it is conveyed by some rapid motions to the mouth.
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.