292 



rigid ossification formed from the vertebral complex (Fig, 21d). Total pairs of 

 pleural ribs 7-9, modally 8. Total vertebrae 46-55 (x = 50.1); total preanal 

 vertebrae 16-20 (x = 18.1) 



Color in Alcohol 



f -1 

 f 





Ageneiosus ucaycdensis is a polymorphic species that exhibits considerable 

 variation in body pigmentation. Coloration patterns range in intensity both within 

 and among populations. Most individuals have an hourglass-shaped patch of 

 melanophores above the occiput that extends lateraUy with short extensions onto the 

 opercula, and anteriorly as long stripes along the edges of the fontanelle, 

 approaching or joined to a crescentic spot on top of the snout. Scattered 

 melanophores on top of rest of head, a small spot just behind eye, and sometimes 

 over top half of operculum. Chin and belly normally immaculate, except for 

 scattered patches of melanophores at origin of paired fins in some individuals. 

 Dorsum with variable pigmentation down back, from dorsal origin to caudal base, 

 ranging from a discrete pair of stripes with an unpigmented middorsal stripe to a 

 small band of irregular dark saddles or blotches (Fig. 51). Pigment of back usually 

 extending onto adipose as a small patch at base. A crescentic spot of variable 

 intensity at base of upper caudal lobe, often accompanied by a smaller round spot 

 near center of lower lobe; distal margin of caudal fin with black margin, often 

 evident only at tips of longest rays. 



Specimens collected from tannin-stained or other dark-water habitats are 

 much more heavily pigmented than described above. Pigmentation in these 

 specimens typically consists of a nearly uniform dense stippling of brown over most 

 of the head and body, diminishing in intensity ventrally to some degree. In addition, 

 the fins often are moderately to deeply pigmented, especially the paired fins, the 



