Fig. 343.—Guitar-fish, Rhinobatus lentiginosus Garman. Charleston, S. C.
Closely related to the Rhinobatidæ are the Rhinidæ (Rhamphobatidæ), a small family of large rays shaped like the guitar-fishes and found on the coast of Asia. Rhina ancylostoma extends northward to Japan.
In the extinct family of Astrodermidæ, allied to the Rhinobatidæ, the tail has two smooth spines and the skin is covered with tubercles. In Belemnobatis sismondæ the tubercles are conical; in Astrodermus platypterus they are stellate.
Rajidæ, or Skates.—The Rajidæ, skates, or rays, inhabit the colder waters of the globe and are represented by a large number of living species. In this family the tail is stout, with two-rayed dorsal fins and sometimes a caudal fin. The skin is variously armed with spines, there being always in the male two series of specialized spinous hooks on the outer edge of the pectoral fin. There is no serrated spine or "sting," and in all the species the eggs are laid in leathery cases, which are "wheelbarrow-shaped," with a projecting tube at each of the four angles. The size of this egg-case depends on the size of the species, ranging from three to about eight inches in length. In some species more than one egg is included in the same case.
Most of the species belong to the typical genus Raja, and these are especially numerous on the coasts of all northern regions, where they are largely used as food. The flesh, although rather coarse and not well flavored, can be improved by hot butter, and as "raie au beurre noir" is appreciated by the epicure. The rays of all have small rounded teeth, set in a close pavement.
Fig. 344.—Common Skate, Raja erinacea Mitchill. Woods Hole, Mass.
Some of the species, known on our coasts as "barn-door skates," reach a length of four or five feet. Among these are Raja lævis and Raja ocellata on our Atlantic coast, Raja binoculata in California, and Raja tengu in Japan. The small tobacco-box skate, brown with black spots, abundant on the New England coast, is Raja erinacea. The corresponding species in California is Raja inornata, and in Japan Raja kenojei. Numerous other species, Raja batis, clavata, circularis, fullonica, etc., occur on the coasts of Europe. Some species are variegated in color, with eye-like spots or jet-black marblings. Still others, living in deep waters, are jet-black with the body very soft and limp. For these Garman has proposed the generic name Malacorhinus, a name which may come into general use when the species are better known. In the deep seas rays are found even under the equator. In the south-temperate zone the species are mostly generically distinct, Psammobatis being a typical form, differing from Raja. Discobatus sinensis, common in China and Japan, is a shagreen-covered form, looking like a Rhinobatus. It is, however, a true ray, laying its eggs in egg-cases, and with the pectorals extending on the snout. Fossil Rajidæ, known by the teeth and bony tubercles, are found from the Cretaceous onward. They belong to Raja and to the extinct genera Dynatobatis, Oncobatis, and Acanthobatis. The genus Arthropterus (rileyi) from the Lias, known from a large pectoral fin, with distinct cylindrical-jointed rays, may have been one of the Rajidæ, or perhaps the type of a distinct family, Arthropteridæ.
Fig. 345.—Numbfish, Narcine brasiliensis Henle, showing electric cells. Pensacola, Fla.