-^/■■'' .■. 129 



procurrent rays, and increased osteological support contributed by the distal tips of 

 the last few preural hemal spines. 



All ageneiosids except A . brevifilis, A . marmoratus, A . pofystictus, and 

 Tetranematichthys have a forked tail with sharply pointed, symmetrical lobes. 

 Ageneiosus pofystictus has the same principal fin-ray count (8 + 9) as the sharply 

 pointed, fork-tailed species, but the fin lobes of this species are broadly rounded, the 

 fin thus appearing moderately emarginate. A forked tail is primitive for catfishes in 

 general (Lundberg and Baskin 1969), so the exceptions listed above are derived with 

 respect to tail morphology. However, an emarginate or truncate tail has evolved 

 independently in many catfishes, so this character state must be interpreted with 

 caution. This is especially true of ageneiosids and auchenipterids. Ferraris (1988) 

 listed several genera of auchenipterids with truncate caudal fins, and he identified, 

 correctly, the homoplasious nature of its occurrence. Among ageneiosids, I consider 

 the presence of a truncate caudal fin to have been independently derived in 

 Tetranematichthys and A. brevifilis. However, I interpret it as a synapomorphy ofyl. 

 brevifilis and A. marmoratus, if in fact these two taxa are distinct from one another 

 (see comments under species account of A. marmoratus). 



Lundberg and Baskin (1969) classified ageneiosids as having a type "B" 

 hypurapophysis, in which the two hypurapophyses fuse to form a horizontal shelf 

 that extends onto the first hypural. To the contrary, most of the specimens that I 

 have examined have the type "C" condition, in which the hypurapophysial shelf 

 extends onto the second hypural. In some species (e.g.,y4. ucayalensis), the degree 

 to which the hypurapophysial shelf extends posteriorly increases during growth, so 

 that in small specimens it appears to end before the second hypural plate, but in 

 larger specimens it extends toward the distal margin of the second hypural. I have 

 not examined the material of A. pardalis on which Lundberg and Baskin (1969) 

 based their conclusion, but it is probable that they had an aberrant or juvenile 

 specimen with an incompletely developed hypurapophysial shelf. The type "C 



