26 



PROCEEDINGS OF THE NATIONAL MUSEUM 



The following counts were made: Number of oblique rows of teeth 

 from middle of jaw to outer edge, upper jaw 15, lower jaw 15; about 

 45 small spines along middle of back behind eyes and on middorsal 

 side of tail. 



Remarks. — This new species appears to be the Atlantic representa- 

 tive of Urotrygon asterias (Jordan and Gilbert) because it has in com- 

 mon with that species a characteristic and definite single row of en- 

 larged spines along the middorsal line of the back and tail. Urotrygon 

 mundus differs from asterias and venezuelae by not having the enlarged 

 spines in a definite continuous row along the midline of the back; 

 instead they are irregularly placed. Measurements made on the types 

 of U. asterias are recorded along with those for U. venezuelae in table 1. 

 It may be distinguished from asterias and from other American rep- 

 resentatives of the genus Urotrygon by means of the key printed by 

 Beebe and Tee Van (Zoologica, vol. 26, pt. 3, p. 264, 1941): 



la. A continuous series of greatly enlarged spines from behind orbits along mid- 

 line of back and tail to base of sting; eye about 3.5 to 4 in snout (Pacific 

 side of Central America) Urotrygon asterias (Jordan and Gilbert) 



lb. Midline of back from behind orbits to just in front of base of tail with a very 

 irregular series of slightly enlarged spines, these arranged in a continuous 

 series on middorsal line of tail to base of sting; eye 5.7 in snout (Gulf of 

 Venezuela) Urotrygon venezuelae, new species 



Table 1. — Measurements, expressed in hundredths of distance from tip of snout to 

 tip of sting, made on two species of Urotrygon 



