Dasyatidæ, or Sting-rays.—In the section Masticura the tail is slender, mostly whip-like, without rayed dorsal or caudal fins, and it is usually armed with a very long spine with saw-teeth projecting backward. In the typical forms this is a very effective weapon, being wielded with great force and making a jagged wound which in man rarely heals without danger of blood-poisoning. There is no specific poison, but the slime and the loose cuticle of the spine serve to aggravate the irregular cut. I have seen one sting-ray thrust this spine through the body of another lying near it in a boat. Occasionally two or three of these spines are present. In the more specialized forms of sting-rays this spine loses its importance. It becomes very small and not functional, and is then occasionally or even generally absent in individuals.
The common sting-rays, those in which the caudal spine is most developed, belong to the family of Dasyatidæ. This group is characterized by the small skate-like teeth and by the non-extension of the pectoral rays on the head. The skin is smooth or more or less rough. These animals lie flat on the sandy bottoms in nearly all seas, feeding on crabs and shellfish. All hatch the eggs within the body. The genus Urolophus has a rounded disk, and a stout, short tail with a caudal fin. It has a strong spine, and for its size is the most dangerous of the sting-rays. Urolophus halleri, the California species, was named for a young man who was stung by the species at the time of its first discovery at San Diego in 1863. Urolophus jamaicensis abounds in the West Indies, Urolophus mundus at Panama, and Urolophus fuscus in Japan. None of the species reach Europe. The true sting-ray (stingaree, or clam-cracker), Dasyatis, is more widely diffused and the species are very closely related. In these species the body is angular and the tail whip-like. Some of the species reach a length of ten or twelve feet. None have any economic value, and all are disliked by fishermen. Dasyatis pastinaca is common in Europe, Dasyatis centrura along our Atlantic coast, Dasyatis sabina ascends the rivers of Florida, and Dasyatis dipterura abounds in the bay of San Diego. Other species are found in tropical America, while still others (Dasyatis akajei, kuhlii, zugei, etc.) swarm in Japan and across India to Zanzibar.
Fig. 348.—Sting-ray, Dasyatis sabina Le Sueur. Galveston.
Pteroplatea, the butterfly-ray, has the disk very much broader than long, and the trivial tail is very short, its little spine more often lost than present. Different species of this genus circle the globe: Pteroplatea maclura, on our Atlantic coast; Pteroplatea marmorata, in California; Pteroplatea japonica, in Japan; and Pteroplatea altavela, in Europe. They are all very much alike, olive, with the brown upper surface pleasingly mottled and spotted.
Sting-rays of various types, Tæniura, Urolophus, etc., occur as fossils from the Eocene onward. A complete skeleton called Xiphotrygon acutidens, distinguished from Dasyatis by its sharp teeth, is described by Cope from the Eocene of Twin Creek in Wyoming. Vertebræ of Urolophus are found in German Eocene. Cyclobatis (oligodactylus), allied to Urolophus, with a few long pectoral rays greatly produced, extending over the tail and forming a rayed wreath-like projection over the snout, is known from the Lower Cretaceous.
Myliobatidæ.—The eagle-rays, Myliobatidæ, have the pectoral fins extended to the snout, where they form a sort of rayed pad. The teeth are very large, flat, and laid in mosaic. The whip-like tail is much like that in the Dasyatidæ, but the spine is usually smaller. The eagle-like appearance is suggested by the form of the skull. The eyes are on the side of the head with heavy eyebrows above them. The species are destructive to clams and oysters, crushing them with their strong flat teeth.
In Aëtobatus the teeth are very large, forming but one row. The species Aëtobatus narinari is showily colored, brown with yellow spots, the body very angular, with long whip-like tail. It is found from Brazil to Hawaii and is rather common.
In Myliobatis the teeth are in several series. The species are many, and found in all warm seas. Myliobatis aquila is the eagle-ray of Europe, Myliobatis californicus is the batfish of California, and Myliobatis tobijei takes its place in Japan.
In Rhinoptera the snout is notched and cross-notched in front so that it appears as if ending in four lobes at the tip. These "cow-nosed rays," or "whipparees," root up the soft bottoms of shallow bays in their search for clams, much as a drove of hogs would do it. The common American species is Rhinopterus bonasus. Rhinoptera steindachneri lives in the Gulf of California.