v'"' . 'r- . ''\ -,..., 290 



Description !i 



Ageneiosus ucayalensis is a medium-sized species, commonly exceeding 200 

 mm SL and reaching a maximum size of 283 mm SL in the material examined. 

 Diagnostic meristic and morphometries of the species are summarized in Tables 21- 

 22. Head greatly flattened and narrow, tapering anteriorly into a spatulate profile 

 when viewed from above or below (Fig. 1). Dorsal profile of head smooth, flat to 

 well-behind orbits, gradually raised above nuchal plate to dorsal spine origin. Eyes 

 large (15% HL in horizontal diameter), sublateral, without free margin and covered 

 by opaque flesh in preserved specimens, frequently with thick subepidermal fat 

 deposits filling adjacent areas of orbital socket. Snout elongate, parabolic, the 

 upper jaw greatly overhanging lower jaw. PremaxiUary tooth band broad in center, 

 curved and gradually tapering to thin points posteriorly, with numerous long, 

 setiform, recurved teeth; most of tooth patch exposed when mouth is closed. 

 Dentaries with patch of teeth similar to premaxillae. Anterior nares remote from 

 edge of upper lip. Skin on head thin, translucent; superficial bones of neurocranium 

 and dorsal portion of brain and cranial nerves, especially optic and olfactory tracts, 

 often visible through skin. Dorsal neurocranial elements thin and delicate, porous 

 in young individuals and without prominent superficial bumps or ridges. Frontal 

 constricted anteriorly, forming deeply zigzagged suture with lateral ethmoid and 

 contributing to large, open orbital area. Sphenotic small plate-like element ' ' 



articulating along short anteromedial margin with frontal and posteromedially with 

 the supraoccipital. Branchiostegal rays 8-11, modally 10. Gill membranes fused to 

 isthmus at or behind plane passing through rear margin of orbit. First gill arch with 

 4-8 rakers in outer row of epibranchial, 12-17 on ceratobranchial; total number of 

 rakers 18-25 (mode = 23; N = 39). Gill rakers long, closely spaced, and generally 

 with accessory cusps on inner margin (Fig. 13a). Barbels short, filiform in all but 



