404 THE PLAGIOSTOMIA. 



Urobatis maculatus, sp. nov. 



Form of U. halleri but differing in the prominence of the fold along each side 

 of the tail and in coloration. Ashy gray with small spots of black, marking the 

 openings of the tubules of the lateral system and the ampullae, and with larger 

 spots of brown, half as large as the eye, symmetrically arranged; a series of 

 about seven beginning in front of each eye and passing back at the inner edge 

 of the outer third of each pectoral, another series of about four spots each begins 

 at each eye and parallels the first about midway between the vertebrae and 

 the outer edge; besides these there is one spot over each gill chamber, one on 

 each half of the shoulder girdle, one over the abdomen at each side of the verte- 

 bral column and one at the axil of the pectoral above the origin of the ventral fin. 

 Faint dark specks appear along the sides of the tail. Outer edges of fins lighter; 

 lower surfaces white. 



One specimen, a mature male, from the U. S. Fish Commission, taken at 

 the head of the Gulf of California, in about nine fathoms. Total length 9g, 

 snout to pores 5, and greatest width 55 inches. 



Urotrygon. 



Urotrygon Gill, 1863, Proc. Acad. nat. sci. Phil., p. 173. 



Disk subcircular, angles and margins rounded, snout produced. Mouth 

 waved; teeth tessellate, numerous, crowns broader than long. Tail longer 

 than body, slender posteriorly, caudal fins narrow, pointed, with a serrated spine 

 near mid length. No dorsal fin. A median series of tubercles. Ventrals 

 subtri angular, anterior rays much longer than posterior, directed laterally. 

 Embryos with a longer strongly curved orbital process and a shorter blunt 

 postspiracular process on the spiracular tegmen. 



Type U. mundus. 



Species of this genus are the most nearly related to the freshwater Potamo- 

 trygons of South America. 



Disk broader than long 

 tail longer than disk 



skin smooth, with median tubercles on back and tail 



brown, with black specks . . . chile?isis (page 405) 

 skin spinose, on snout, median tubercles on back 



brown, uniform goodei (page 405) 



