• 228 

 Color in Alcohol 



Top of head and dorsum with a dense cast of slate-gray melanophores, 

 diminishing sublaterally (Fig. 41). The intensity and extent of pigmentation is 

 variable, but never appearing mottled and almost always including dense patches of 

 dusky specks on the chin, the flanks above the anal fin, and an elongate streak in 

 each caudal lobe extending from the base of the hypural plate to the midpoint of the 

 longest caudal rays or beyond. Pigment on the chin ranges from a full semicircle of 

 dense specks extending from the lower lip to the rear margins of the orbits, to a faint 

 crescent overlying the dentaries, and invariably represented by at least traces of 

 subcutaneous flecks scattered between the symphysis of the dentaries. Fresh 

 specimens have deep black on the lips, chin, and flanks above the anal fin, and have 

 streaks through each lobe of the caudal fin. In most specimens there is a diffuse 

 oval patch of minute, superficial melanophores on the flank between the lateral line 

 and the base of the anal fin. 



Distribution 



Ageneiosus atronasus is distributed throughout the middle and upper Amazon 

 River basin, including the Rfo Ucayali in Peru, the Rio Mamore in Bolivia, and 

 other major drainages of the Rio Solimoes and upper Rio Amazonas in Brazil (Fig. 

 42). The species has been taken principally from the large main channels and 

 sloughs associated with lowland lotic habitats throughout its range. Of the material 

 examined, the farthest downstream record in the Amazon basin is from the Rio 

 Maica, just below the mouth of the Rio Tapajos, but additional collecting is needed 

 to determine the eastern extent of the species' range. 



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