24 PROCEEDINGS OF THE NATIONAL MUSEUM vol.99 



alcohol brown with numerous small white spots everywhere on dorsal 



surface (fig. 1) - Urobatis sloani (Blainville)' 



2b. Caudal fin narrow, long, and tapering to a point (end of tail usually missing 

 in adults) and without rays; eye and spiracle about lYs in interorbital 

 space; distance from front of oronasal groove to corner of upper Up con- 

 tained about lYs in width of nasal flap; eye moderate about 2}4 in inter- 

 orbital space and 4 in snout; a series of rather strong spines along mid- 

 dorsal line of tail in front of sting; middle gill slit, about equidistant 

 between tip of snout and center of anus; color in alcohol brownish or 

 blackish dorsally, tail with bars or underside sometimes blotched; outer 

 part of disk on ventral side grayish to brownish — fresh-water species. 

 (Potamotrygon.) 

 3a. Coloration of ventral side of disk mottled with brownish; sides of tail 

 in front of sting with regularly placed pale roundish to oblong spots 

 and behind base of sting barred with pale spots (Amazon and 



Guianas) Potamotrygon hystrix (Muller and Henle) 



36. Coloration of ventral side of disk plain pale, the margins of disk plain 



darkish to pale grayish, not mottled. 



4a. Sides of tail in front of sting mottled but not with regularly placed 



pale or whitish oval spots; tail behind base of sting nearly plain 



black without definite pale bars (Magdalena, Atrato, and Maracaibo 



Basins) Potamotrygon magdalenae (Dum^ril) 



45. Sides of tail in front of sting with regularly placed pale or whitish oval 

 to roundish spots; tail behind base of sting with distinct pale bars 

 (Orinoco Basin) Potamotrygon humboldtii (Dum^ril) 



Genus UROTRYGON Gill 



Urotrygon Gill, Proc. Acad. Nat. Sci. Philadelphia, 1863, p. 173. (Genotype, 

 Urotrygon mundus Gill, U.S.N.M. No. 7297, west coast of Central America.) 



UROTRYGON VENEZUELAE, new species 



Stingray; Raya de agtja salada 

 Figure 2 



Holotype. — U.S.N.M. No. 121966, a female measuring 255 mm. 

 from tip of snout to tip of tail, collected by the U. S. S. Niagara in the 

 Gulf of Venezuela at Point Macolla, April 19, 1925. 



Description (of only known specimen). — Width of disk a little 

 greater than the length of disk from tip of snout to its posterior margin 

 not including pelvic; snout a little produced so that at each side of 

 snout the outline is a little concave, then convex; outline of pelvic fins 

 rourded, completing the circular ouUine of the disk; center of anus to 

 tip of tail equal to distance from tip of snout to rear margin of pel vies; 

 length of snout 3.4 in snout to center of anus; least interorbital width 

 2% in snout; middle gill sht equidistant between tip of snout and center 

 of anus; base of sting closer to tip of tail than to anus by twice diameter 

 of eye; eye 2.4 in interorbital space, and about 5.7 in snout; caudal fin 

 moderately narrow, the greatest height of caudal fin about equal to 

 diameter of eye; interorbital space a little concave; back everywhere 



• Not yet reported from Venezuelan waters. 



