Page:Encyclopædia Britannica, Ninth Edition, v. 20.djvu/317

Rh RAY 299 RAY. The Rays (Batoidei) together with the Sharks (Selac/toidei) form the suborder Plagiostomata of Cartila- ginous fishes, and are divided into six families, as already noticed in ICHTHYOLOGY, vol. xii. pp. 685, 686. The first family contains only the Saw-fishes (Pristis), of which five species are known, from tropical and subtropical seas. Although saw-fishes possess all the essential characteristics of the rays proper, they retain the elongate form of the body of sharks, the tail being excessively muscular and the sole organ of locomotion. The protruding intestines. The "saw" (fig. 1) is a flat and enormously devel- oped prolongation of the snout, with an endo- skeleton which consists of from three to five carti- laginous tubes ; these are, in fact, merely the rostral processes of the cranial cartilage and are found in all rays, though they are commonly much shorter. The integument of the saw is hard, covered with shagreen ; and a series of strong teeth, sharp in front, and flat behind, are embedded in it, in alveolar sockets, on each side. The saw is a most formidable weapon , of offence, by means of which the fish tears pieces of flesh off the body of its victim, or rips open its abdomen to feed on the teeth proper, with which the mouth is armed, are ex- tremely small and obtuse, and unsuitable for inflicting wounds or seizing animals. Saw-fishes are abundant in the tropics ; in their stomach pieces of intestines and frag- ments of cuttle-fish have been found. They grow to a large size, specimens with saws 6 feet long and 1 foot broad at the base being of common occurrence. The rays of the second . family, Rhinobalidas, bear a, strong resemblance to the saw -fishes, but lack the ' saw. Their teeth are con- flat, obtuse, and adapted for crushing hard-shelled mar- ine animals. There are about sixteen species, from k tropical seas. Fia. 1. Pristis perrotteti. The third family, Torpcdinidss, includes the Electric Rays. The peculiar organ (fig. 2) by which the electricity is produced has been described in vol. xii. p. 650. The fish uses this power voluntarily either to defend itself or to stun or kill the smaller animals on which it feeds. To receive the shock the object must complete the galvanic circuit by communicating with the fish at two distinct points, either directly or through the medium of some conducting body. The electric currents created in these fishes exercise all the other known powers of electricity : they render the needle mag- netic, decompose chemical compounds, and emit the spark. The dorsal surface of the electric organ is positive, the ventral negative. Shocks accidentally given to persons are severely felt, and, if pro- ceeding from a large healthy fish, will temporarily paralyse the arms of a strong man. The species of the genus Torpedo, six or seven in number, are distributed over the coasts of the Atlantic and Indian Ocean, and two reach northwards to the coasts of Great Britain (T. marmorata and T. hcbetans). They are said to attain to a weight of from 80 to 100 Ib, but fortunately such gigantic specimens are scarce, and prefer sandy ground at some distance from the shore, where they are not disturbed by the violent agita- tion of the surface-water. Other genera, comprising species of smaller size, inhabit different parts of the tropical and subtropical FIG. 2. Torpedo tmrce (Mediterranean). A portion of the skin on the left side has been removed to show the electric organ. seas. All the rays of this family have, like electric fishes generally, a smooth and naked body. The fourth family, Raiidss, comprises the Skates and Rays proper, or Raia. More than thirty species are known, chiefly from the temperate seas of both hemispheres, but much more numerously from the northern than the southern. A few species descend to a depth of nearly 600 fathoms, without, however, essentially differing from their surface congeners. Rays, as is sufficiently indicated by the shape of their body, are bottom-fishes, living on flat sandy ground, generally at no great distance from the coast or the surface. They lead a sedentary life, progressing, like the flat-fishes, by an undulatory motion of the greatly extended pectoral fins, the thin slender tail having entirely lost the function of an organ of locomo- tion, and acting merely as a rudder. They are carnivorous and feed exclusively on molluscs, crustaceans, and fishes. Some of the species possess a much larger and more pointed snout than the others, and are popularly distinguished as "skates." The follow- ing are known as inhabitants of the British seas : (a) Short- snouted species : (1) the Thornback (R. clavata), (2) the Homelyn Ray (R. maculata), (3) the Starry Ray (R. radiata), (4) the Sandy Ray (R. circularis) ; (b) Long-snouted species, or Skates : (5) the Common Skate (R. batis), (6) the Flapper Skate (R. macrorhynchus), (7) the Burton Skate (R. marginata), (8) and (9) the Shagreen Skates (R. vomer and R. fullonica). A deep-sea species (R. hyper- borea) has recently been discovered near the Faroe Islands at 600 fathoms. Most of the skates and rays are eaten, except during the breeding season ; and even the young of the former are esteemed as food. The skates attain to a much larger size than the rays, viz., to a width of 6 feet and a weight of 400 and 500 Ib. The members of the fifth family, Trygonidse or Sting-rays, are distinguished from the rays proper by having the vertical fins replaced by a strong spine attached to the upper side of the tail. Some forty species are known, which inhabit tropical more than temperate seas. The spine is barbed on the sides and is a most effective weapon of defence ; by lashing the tail in every direction the sting-rays can inflict dangerous or at least extremely painful wounds. The danger arises from the lacerated nature of the wound as well as from the poisonous property of the mucus inoculated. Generally only one or two spines are developed. Sting-rays attain to about the same size as the skates and are eaten on the coasts of the Mediterranean and elsewhere. One species (Trygon pastinaca] is not rarely found in the North Atlantic and extends northwards to the coasts of Ireland, England, and Norway.
 * sequently more developed,