POTAMOTRYGON HUMEROSUS. 419 



POTAMOTRYGON CIRCULARIS, Sp. nov. 

 Plate 31, fig. 1, 2; Plate 54, fig. 1 (pelvis); Plate 70, fig. I, 2 ^skeleton). 



Disk nearly round, little longer than broad. Mouth small, regularly curved, 

 in width about two fifths of the distance from the end of the snout, with five 

 papillae at the bottom. Teeth small, white on one specimen partly black on 

 another, with concave crowns and sharp inward edges with a sharp angle or 

 angles (on males); in |§ rows. Eyes small, prominent, distant from the an- 

 terior margin nearly twice their distance apart. Spiracles twice as large as the 

 eyes, interspiracular distance nearly two thirds of the length of the snout from 

 the ej^es. Ventrals broad and broadly rounded on the posterior border. Tail 

 strong and depressed in the base, with a weak fold at each side, and slender and 

 compressed behind the spine with a low cutaneous fold above and another below. 

 From the abdominal pores to the caudal spine is two thirds of the length of the 

 body to the pores. Back and tail rough with small stellate-based spines, larger 

 toward the middle of the back. One or more large tubercles, rounded, ridged 

 and much swollen in the base, and compressed and hooked in the short cusp, 

 occur on each shoulder; others appear in an irregular series from above the 

 middle of the abdomen to the caudal spine, in a row of smaller ones along each 

 side of the base of the tail and in an irregular series or band around the sides 

 and the forward part of the disk near the margin. The bases of the tubercles 

 are much swollen and ridged, and in places a number of them are fused into a 

 broad plate; the cusps are small. 



Greyish brown with faint mottlings and spots of lighter and of darker, 

 smaller toward the edges. The young appear to be light oUve or yellowish 

 profusely spotted with rounded spots slightly darker or reddish. Lower surface 

 chocolate-brown with blotches of white below the gills and anteriorly. The 

 young are more nearly white on the lower surfaces. 



Length of disk in one specimen 14|, width 14^; in another the length is 

 16|, and the width 16 inches. 



Teffe, Brazil. Thayer Expedition. 



POTAMOTRYGON HUMEROSUS, Sp. nOV. 



Disk oval, longer than wide, snout from the eyes longer than the greatest 

 distance between the spiracles. Mouth moderate, width about two thirds of 

 the distance from the end of the snout, with five papillae, curves not abrupt. 



