Suborder Batoidei, or Rays.—The suborder of Batoidei, Rajæ, or Hypotrema, including the skates and rays, is a direct modern offshoot from the ancestors of tectospondylous sharks, its characters all specialized in the direction of life on the bottom with a food of shells, crabs, and other creatures less active than fishes.
The single tangible distinctive character of the rays as a whole lies in the position of the gill-openings, which are directly below the disk and not on the side of the neck in all the sharks. This difference in position is produced by the anterior encroachment of the large pectoral fins, which are more or less attached to the side of the head. By this arrangement, which aids in giving the body the form of a flat disk, the gill-openings are limited and forced downward. In the Squatinidæ (angel-fishes) and the Pristiophoridæ (sawsharks) the gill-openings have an intermediate position, and these families might well be referred to the Batoidei, with which group they agree in the tectospondylous vertebræ.
Other characters of the rays, appearing progressively, are the widening of the disk, through the greater and greater development of the fins, the reduction of the tail, which in the more specialized forms becomes a long whip, the reduction, more and more posterior insertion, and the final loss of the dorsal fins, which are always without spine, the reduction of the teeth to a tessellated pavement, then finally to flat plates and the retention of the large spiracle. Through this spiracle the rays breathe while lying on the bottom, thus avoiding the danger of introducing sand into their gills, as would be done if they breathed through the mouth. In common with the cyclospondylous sharks, all the rays lack the anal fin. The rays rarely descend to great depths in the sea. The different members have varying relations, but the group most naturally divides into thick-tailed rays or skates (Sarcura) and whip-tailed rays or sting-rays (Masticura). The former are much nearer to the sharks and also appear earliest in geological times.
Pristididæ, or Sawfishes.—The sawfishes, Pristididæ, are long, shark-like rays of large size, having, like the sawsharks, the snout prolonged into a very long and strong flat blade, with a series of strong enameled teeth implanted in sockets along either side of it. These teeth are much larger and much less sharp than in the sawsharks, but they are certainly homologous with these, and the two groups must have a common descent, distinct from that of the other rays. Doubtless when taxonomy is a more refined art they will constitute a small suborder together. This character of enameled teeth on the snout would seem of more importance than the position of the gill-openings or even the flattening and expansion of the body. The true teeth in the sawfishes are blunt and close-set, pavement-like as befitting a ray. (See Fig. 152.)
Fig. 342.—Sawfish, Pristis pectinatus Latham. Pensacola, Fla.
The sawfishes are found chiefly in river-mouths of tropical America and West Africa: Pristis pectinatus in the West Indies; Pristis zephyreus in western Mexico; and Pristis pectinatus in the Senegal. They reach a length of ten to twenty feet, and with their saws they make great havoc among the schools of mullets and sardines on which they feed. The stories of their attacks on the whale are without foundation. The writer has never found any of the species in the open sea. They live chiefly in the brackish water of estuaries and river-mouths.
Fossil teeth of sawfishes occur in abundance in the Eocene. Still older are vertebræ from the Upper Cretaceous at Maestricht. In Propristis schweinfurthi the tooth-sockets are not yet calcified. In Sclerorhynchus atavus, from the Upper Cretaceous, the teeth are complex in form, with a "crimped" or stellate base and a sharp, backward-directed enameled crown.
Rhinobatidæ, or Guitar-fishes.—The Rhinobatidæ (guitar-fishes) are long-bodied, shovel-nosed rays, with strong tails; they are ovoviviparous, hatching the eggs within the body. The body, like that of the shark or sawfish, is covered with nearly uniform shagreen. The numerous species abound in all warm seas; they are olive-gray in color and feed on small animals of the seabottoms. The length of the snout differs considerably in different species, but in all the body is relatively long and strong. Most of the species belong to Rhinobatus. The best-known American species are Rhinobatus lentiginosus of Florida and Rhinobatus productus of California. The names guitar-fish, fiddler-fish, etc., refer to the form of the body. Numerous fossil species, allied to the recent forms, occur from the Jurassic. Species much like Rhinobatus occur in the Cretaceous and Eocene. Tamiobatis vetustus, lately described by Dr. Eastman from a skull found in the Devonian of eastern Kentucky, the oldest ray-like fish yet known, is doubtless the type of a distinct family, Tamiobatidæ. It is more likely a shark however than a ray, although the skull has a flattened ray-like form.
