POTAMOTRYGON MAGDALENAE. 121 



sevenths of the distance from sin ml to pores. Tail behind (lie spine compressed, 

 sharp keeled on the top, with a low membranous fold above and a narrower 

 one below. 



Back brown, darker from the head backward, thickly marked with round 

 spots of light color, some of them united into short bands. Near the outer edge 

 of the disk and parallel with it there is a series of about twenty spots of the 

 lighter color each of which has a crescent-shaped spot of blackish at its outer 

 edge, on openings of pores; inside of this series the spots are larger. Individuals 

 vary in regard to size of spots, on the larger one described above they are smaller 

 than on the other and the brown color forms a net-work somewhat resembling 

 that on P. magdahnae. Lower surface of disk white, darker toward the hinder 

 margins; lower surface of tail blotched and clouded with brown, darker back- 

 ward. 



One specimen has a length of disk of 6, and a width of 5j inches, another, 

 a mature male, measures 85 inches in length of disk and 7\ in width. 



Two specimens were secured by Prof. L. Agassiz, the Thayer Expedition, 

 from the Rio Poty a tributary of the Paranahyba River, Brazil, and a third from 

 the Paranahyba at San Gongallo. 



POTAMOTRYGON MAGDALENAE. 



Taeniura 7iiagdalenae Dumeril, 1865, Elasm., p. 625; Steindachner, 1878, Denk. Akad. wiss. Wien, 



39, p. 72, pi. 15. 

 Potnmolryon magdahnae Eigenmann, 1892, Proc. U. S. nat. mus., 15, p. 25; Steindachner, 1902, 



Denk. Akad. wiss. Wien, 72, p. 148. 



Disk oval, little longer than wide, snout with a slight prominence. Mouth 

 small, with five papillae; teeth flat. Tail longer than the disk, with a cutaneous 

 fold above and another below, and with a median series of compressed hooked 

 tubercles in front of the spine. Back rough with numerous small asperities, 

 among which larger blunter tubercles are mixed, smaller toward the margins. 



Brown with lighter yellowish spots, as large as the eye and smaller, so 

 numerous and close together that the brown appears as a net-work over the disk 

 and tail. 



Closely allied to P. hystrix and P. motoro, but distinguished by the colora- 

 tion and by the armature; the base of the tail being without lateral series of 

 tubercles. 



Magdalena River. 



