1877.] 213 [Garman. 



In shape and thickness of disk this species is intermediate between 

 Humboldtii and Dumerilii; it is readily distinguished from either by 

 the teeth, which are much larger and differently shaped. 



Twenty-nine specimens from various localities. 



Potamotrygon Dumerilii. 



Ellipesurus spinicauda Sehomburgk, Fish. Brit. Guiana, II, p. 

 184, pi. xxiii. 



Trygon (Tcenura) Dumerilii Castelnau, Anim. Amer. Sud, Poiss., 

 p. 101, pi. 48, f. 1. 



Ellipesurus spinicauda Dumeril, Elasmobranchs, p. 582. 



Tceniura Dumerilii Dum., 1. c, p. 622. 



Ellipesurus spinicauda Giinther Cat., viii, p. 472. 



Disk subcircular, nearly as broad as long, retaining its width pos- 

 teriorly. Head broad, flattened. Snout with a prominence. Eyes 

 small, prominent. Spiracles large, immediately behind the eyes. 

 Mouth curved, indentation in -the upper jaw shallow, with five 

 papilla?. Teeth equal, very small, the inner edge prominent and 

 bearing three cusps, upper surface concave, bases pentagonal, with 

 the outer angles rounded and the outer side concave, in twenty-six 

 to forty-four series — according to age — in the upper band. Poste- 

 rior angles of pectorals rounded. Ventrals triangular, with rounded 

 extremities. Tail broad, depressed, with a serrated spine at a dis- 

 tance from the ventrals equal to more than half the length of the 

 body; slender posteriorly, compressed into a keel on its upper half, 

 lower half round, with narrow cutaneous expansions above and below. 



Young naked, yellowish, with brown lines or spots, light colored 

 on lower surface. 



Medium sized brownish, with rounded spots of light color, cov- 

 ered with small sharp scales on the back, with a dorsal and two 

 lateral rows of spines on the tail. 



Large examples brown, spots nearly or quite obsolete, entirely 

 covered on the dorsal surface with scales, with very large swollen- 

 based sharp-pointed tubercles of irregular sizes and shapes on each 

 shoulder, in the median and lateral rows on the tail, and in a band 

 around the disk near the margin. 



On specimens before me some of the tubercles are more than an 

 inch in diameter and bear from one to half a dozen points; some of 

 the caudal tubercles measure three quarters of an inch in length of 

 base and in height. 



