CHAPTER VIII. 



SYSTEMATIC ACCOUNT OF THE FRESHWATER FISHES 



OF BRITISH GUIANA. 



Class SELACHII. 



Order BATOIDEI. 



Suborder MASTICURA. 



Whip-tailed Rays. 



Family I. DASYATID/E. 

 Tail abruptly slender, its back usually with a serrated spine; 'pectoral fins 

 uninterrupted, confluent around the snout; teeth small; nasal valves forming a 

 flap, which is joined to the upper jaw by a narrow frenum; spiracles large. 



Subfamily Potamotrygonin^e. 

 Pelvis with a sword-shaped cartilage extending forward in the mid-ventral line. 



Key to the Guiana Genera of Potamotrygonin.e. 

 a. Tail with irregular thorns on its upper surface, and with a large spine. 



6. Mouth with papillae; teeth in more than twenty-five rows Potamotrygon. 



bb. Mouth without papilla 1 ; teeth in less than twenty-five rows Paratrygon. 



aa. Tail with many short spines about its base Elipesurus. 1 



Potamotrygon Garman. 

 Tceniura Muller and Henle, Bericht. K. Preuss. Akad. Wiss., 1837, 117 (ornatum). 

 Potamotrygon Garman, Proc. Bost. Soc. Nat. Hist., 1877, 210. 

 Type, Pastinaca humboldtii Roulin. 



1. Potamotrygon hystrix (Muller and Troschel). 

 ? Pastinaca humboldtii Roulin, Ann. Sc. Nat,, XVI, 1829, 104, pi. 3 (Meta).- 



Dumeril, Hist. Nat. Poiss., I, 1865, 625 (copied). 

 Potamotrygon humboldtii Garman, Proc. Bost, Soc. Nat. Hist., 1877, 210. 

 Trygon hystrix Muller and Henle, Syst. Beschr. Plagiostomen, 1841, 167. — Val- 



1 Elipesurus was taken by Schomburgk in the Rio Branco, and may occur in the Essequibo basin also. 



116 



