Fishes of the Western North Atlantic 417 



than body in most; tail witli a large saw-edged spine (or spines). Front of cranium 

 weakly indented in midline, its outer corners broadly rounded. Pelvis moderately arched 

 in subangular contour, without median process. Surfaces of gill arches smooth inward 

 from gill filaments. Characters otherwise as in the Dasyatidae. 



Remarks. All of these small Rays, the largest only about 30 inches long, are much 

 alike in general appearance. They are inhabitants of moderately shoal water from only 

 a few feet down to about 30-40 fathoms, ^^ perhaps deeper. When they are in water 

 shallow enough for observation, they are commonly found partly buried in the sand or 

 mud of the bottom, and, like their longer-tailed relatives of the family Dasyatidae, they 

 are said to scoop out holes in the sand with their pectoral fins, thus dislodging worms 

 and crustaceans on which they feed. In some places they are so numerous in shoal water 

 that the bottom can almost be described as paved with them. Under such circumstances 

 they are dangerous to fishermen wading on the flats, for they are well armed and it is 

 probable that their tail spines are venomous, as are those of the long-tailed Sting Rays, 

 though this has not actually been tested for them by clinical experiment. 



Range. The geographic range of the family includes: the western Pacific from 

 Japan and Korea to southern Australia and Tasmania, including the East Indies; the 

 coasts of the eastern Pacific from southern California (Cape Conception) to Chile; and 

 the western Atlantic from Florida (occasionally North Carolina) to the southern side of 

 the Caribbean and perhaps farther south along the Atlantic Coast of South America.^^ 



Recent synopses credit the western Pacific area with ten species, ^^ the eastern side 

 of the Pacific with nine,*^ while only three are known in the western Atlantic. Up to 

 the present time, no member of the family has been reported either from the eastern 

 side of the Atlantic or from the Indian or African coasts of the Indian Ocean. 



Key to Genera 



I a. A small dorsal fin on tail anterior to spine in both adults and embryos. 



Trygonoptera Miiller and Henle 1841. 

 Tasmania, Australia, East Indies. 

 I b. No dorsal fin in adults, though one is sometimes present in embryos. 



2a. Caudal fin not more than ^6 ^s broad as long; tail a little longer than body, 



each measured from center of cloaca. Urotrygon Gill 1863, p. 427. 



2b. Caudal fin more than 1/4 as broad as long; tail no longer than body, each 



measured from center of cloaca. Urolophus Miiller and Henle 1837, p. 418. 



Remarks on Generic Definitions. Two recent authors, not using the dorsal fin as a 

 basis for generic separation in this family, unite in Urolophus the two groups of species 

 that are divided here between Urolophus and Trygonoptera.^^ However, we think it wiser 



81. Thirty-three fathoms is the greatest depth for which we have found definite records of one of this group. 



82. For further comment on this point, see p. 426. 83. Fowler, Bull. U.S. nat. Mus., 100 {13), 1941: 440. 



84. Beebe and Tee-Van, Zoologica N. Y., 26, 1941: 264-271. 



85. Whitley (Fish. Aust., i, 1940: 215-219); Fowler (BuU. U. S. nat. Mus., 100 [13], 1941: 439). The latter author 

 recognizes two subgenera, Urolophus and Trygonoptera, separated by the length of the tail, however, and not by the 

 presence or absence of a dorsal fin. 



