MYLIOBATIDAE. 427 



Ventrals covered by the pectorals, subtriangular, outer rays longer, angles 

 rounded. Tail less than one and one half times as long as the disk, depressed, 

 with a serrated spine close to the body; base short, irregularly armed above by 

 subcorneal broad-based tubercles; filiform in the posterior portion with low 

 cutaneous folds above and below, more distinct on the young. Young smooth; 

 older ones rough with small sharp-cusped scales the bases of which have radiating 

 ridges also with sharp cusps. The tubercles vary greatly in number and size; 

 the bases are more or less swollen and fused into plates each bearing a number 

 of cusps. Length of disk 8.8, greatest width 7.7, tail from vent 13.3 inches. 



Back light yellowish brown irregularly marked with spots and streaks of 

 brown, Plate 34, more uniform rusty brown with age; lower surfaces white, 

 clouded or blotched with brown on large individuals. 



Secured by the Thayer Expedition at Obidos, Manaos, and Para, Brazil. 



A second species of this genus is accounted for by a photograph and meas- 

 urements furnished by Professor Eigenmann. Compared with D. thayeri it is 

 more elongate and more narrowed toward each end of the disk ; the width of the 

 disk is five sixths of the length, and eyes, spiracles, and mouth are nearer to the 

 front margin, which is not concave. The tail is very short, probably mutilated; 

 its base tapers rapidly, at its end bears a couple of serrated spines, and is armed 

 on its forward portion by a median series of half a dozen strong tubercles which 

 posteriorly are flanked by three similar ones on each side. Smaller tubercles 

 appear behind the spines. 



Color nearly uniform brownish. Length of disk 2I5, width 17.7 and length 

 of tail 5.11 inches. 



The form appears to be intermediate between those of Elipesurus spinicauda 

 of Schomburgk and Disceus thayeri; it differs from the former in that the eyes and 

 spiracles are farther back, that the spiracle has the process on its outer border, 

 and that the tail is provided with a serrated spine. 



The locality given is the Jurua river, a southwestern affluent of the Upper 

 Amazon above Teffe. 



Myliobatidae. 



Body, head, and pectorals forming a broad lozenge-shaped disk. A pair 

 of rostral fins, joined in front of the snout, either separated from the pectorals 

 or connected with them at the side of the head. Teeth angular, broad, flat, 

 tessellated, median series commonly broader than the laterals, if any. Eyes 

 prominent, lateral. Spiracles large, behind the eyes, opening laterally. Cra- 



