peak nuptial males oiA. brevifilis that were examined had the odontodes arranged 

 in the above fashion, whereas in A. atronasus and^. n. sp., the serrae are distributed 

 along the entire anterior margin of the spine. However, limited material of nuptial 

 males, and incomplete information about the development and hypertrophy of the 

 dimorphic spine, precludes a thorough taxonomic comparison among species at 

 present. ., . ■; ; .^.^; . . 



In all species, the distal tip of the defensive dorsal-fin spine beyond the 

 posterior ossified portion is continued as a short, segmented, membranous ray. In 

 A. brevifilis and^. mannoratus, the entire spine is segmented, flexible, and 

 unserrated in all but breeding males. A somewhat intermediate condition between 

 these two species and all other species is found mA.polystictus, in which 

 approximately the distal one-third of the spine is relatively feeble. Reduced 

 ossification of the dorsal-fin spine of these species is a derived condition, relative to 

 all other ageneiosids and the majority of other catfishes. This condition has 

 occurred independently in several unrelated catfish groups, including some clariids 

 and pimelodids. : l "'* , '^ t 



In^. brevis, the spine is relatively short and stout, with prominent lateral 

 ridges and rugosities, especially near the base. In addition, the posterior odontodes 

 are somewhat stronger than in other species, and are often bifurcated or spUt into 

 two rows proximally. The relatively strong spine oiA. brevis is presumably 

 somewhat more primitive than that of other species. The odontodes along the rear 

 margin of the spine in most other species are somewhat longer and lanceolate- 

 shaped, although in Tetranematichthys the serrae are relatively weak. 



In ageneiosids, the basal support of the dorsal fin is intimately associated 

 with the rear of the neurocranium and the front of the vertebral colunm, as is the 

 case in other doradoids. There is considerable confusion of terminology associated 

 with these basal elements, however, which deserves further comment. 



