176 GENUS TRYGON. 



these entirely fresh-water skates may be found to 

 vary considerably in their structure and economy. 

 Of the first, our author thus writes : 



" "We are informed by Linnaeus that the Rai/a^ 

 or Rays, are exclusively inhabitants of the seas. I 

 think a species has since been described by D'Or- 

 bigny as inhabiting fresh-water rivers ; Guiana, 

 however, possesses several species, which conse- 

 quently will prove new to Ichthyology. Their form 

 is not different from those of the salt-water rays, 

 and they are generally armed with spines; some 

 with the back more or less spiny, tuberculous, or 

 smooth. The spine or prickle, in the fresh- water 

 Trygon is an equally dangerous weapon as that of 

 its congeners which inhabit the sea, and wounds 

 inflicted with it cause frequently severe inflamma- 

 tion. As they generally frequent such places of the 

 river where the bottom is sandy, and in which they 

 bury themselves, in order the easier to entrap their 

 prey, the Indians use the greatest precaution when 

 they are obliged to draw their canoes over such 

 shallow places. I have known several instances 

 where, nevertheless, wounds have been inflicted, 

 and a swelling of the part, and in some instances 

 feverish symptoms have been the consequence. The 

 Indians use sometimes the leaves of the aromatic 

 guava (Pisldium parviflorum, Beuth), which grows 

 so abundantly among the rocks in the rivers of the 

 interior, and after having pounded them, they are 

 put on the wound, but I do not think with much 

 eflect, at least not in those cases where I saw it 



