424 



THE PLAGIOSTOMIA. 



POTAMOTRYGON BRACHYURUS. 



Trygon brachyurus Gunther, 1880, Ann. mag. nat. hist., sor. 5, 6, p. 8. 



Potamotrygon brachyurus Eigenmann, 1892, Proc. U. S. nat. mus., 15, p. 25 (name only). 



Disk broader than long. Eyes small, length two fifths of the width of the 

 skull between them. Spiracles about twice the size of the orbit. Mouth with 

 five papillae. Tail much shorter than the body, with a low fold above, behind 

 the spine, and a lower one below; with a series of small tubercles on the median 

 hne in front of the caudal spine. 



Back greyish brown with a coarse net-work of blackish streaks; white 

 below, with blackish margins. 



Length of disk 10, of tail 9, and greatest width 12 inches. 



Buenos Aires. 



The measurements given by Gunther make this species and the next follow- 

 ing differ from all others in the genus by being broader than long in the disk, in 

 which they agree with Dasybatus rather than Potamotrygon. Further details 

 are necessary before they can be placed with any degree of certainty. 



Potamotrygon reticulatus. 



Trygon hystrix GtJNTH., 1870, Cat. fishes Brit, mus., 8, p. 482 (part). 



Trygon reticulatus Gijnther, 1880, Ann. mag. nat. hist., ser. 5, 6, p. 8. 



Potamotrygon reticulatus Eigenmann, 1892, Proc. U. S. nat. mus., 15, p. 25 (name only). 



Eilipesurus reticulatus Ribeiro, 1907, Arch. Mus. nac, 14, p. 185. 



Disk ovate, rounded in front. Mouth with four papillae at the bottom. 

 Eyes of moderate size, half as wide as the skull between them. Spiracles 

 nearly twice the width of the orbit. Back with small stellate-based asperities; 

 margins of disk smooth. A series of irregularly arranged moderate sized 

 tubercles on the median line of the tail. Tail much longer than the disk, with 

 a low fold above, behind the spine, and a lower one below. 



Back brown with a net-work of wide hexagonal meshes in black lines; 

 white below. 



Length of disk 7l, tail 12, and greatest width 8^ inches. 



Surinam. 



Elipesurus. 



Elipesurus Schomburgk, 1843, Fishes Guiana, 2, p. 184. 



This genus, with its type species E. spinicauda, was reproduced by Sir 

 William Jardine from Schomburgk's notes and drawing. It was not specially 



