All these rays should be considered 'true' Histrix based on the information given in the scientific description of P. Histrix, originally recorded in Buenos Aieres, Argentina.. correct?
What hobbyist consider a 'true' Histrix from Rio Negro in Brazil, is obviously not pictured.. perhaps we should start referring to the Rio Negro Histrix as Potamotrygon sp. "C" or Potamotrygon cf. Histrix with the emphasis on the cf. (meaning compared to, but not justified as a new species) .. I believe in all the scientific .pdf white papers they refer to the Rio Negro Histrix as Potamotrygon sp. "C" or 'arraia cururu' - or Cururu Ray by the locals. (http://209.85.141.104/search?q=cach....+C&hl=en&ct=clnk&cd=5&gl=us&client=firefox-a)