^"■' -!><.• JK.'' ''-!'<■ 



293 



anal, and the base of the caudal. Certain populations, especially those occupying 

 rivers draining the Guiana shield, consistently have such a darker pigmentation 

 pattern. .,. \.' • 



■•' ■■''''. '' •;■ : .... 



Distribution / - ;'\ - ■ ^ 



*.■ ' .' . t V V ;;■■ ;,■■ , ■■■- - 



Ageneiosus ucayalensis is a widespread species, paralleling ^4. brevifilis in 

 terms of the size of its entire geographic distribution (Fig. 52). It is found 

 throughout most of the major lowland drainages of South America, including the 

 Orinoco and Amazon basins and various river systems draining directly into the 

 Atlantic Ocean in the northeastern portion of the continent. It is not present in any 

 of the trans-Andean rivers of northwestern Venezuela or Colombia, and apparently 

 does not enter the Rio Sao Francisco of eastern Brazil, It is present, however, in the 

 upper reaches of the Rio Tapajos, as well as in the Rio Parand drainage. 



Etymology • ;.• 



The specific epithet is derived from the Rio UcayaU of Peru, where the 

 holotype was collected. 



Common Names • ". 



Brazil: ximb6, fidalgo, patinha (Smith 1981, Santos et al. 1984). Venezuela: 

 bagre zapato (Novoa 1982 [fig. 43] mislabelled ^4. brevifilis]). 



