The lowest branchiostegal count (seven) is found in A. piperatus. Tetranematichthys 

 has ten to twelve branchiostegals, but too few specimens were examined to 

 accurately determine a modal count for this species. Among catfishes in general, 

 high branchiostegal counts are considered derived (Gosline 1973, Lundberg 1982). 

 However, most catfishes have between nine and eleven (Howes 1983), which is a 

 range that is entirely within the intraspecific variation that I have observed in some 

 species of ageneiosids. In some catfishes, an increase in the number of 

 branchiostegal rays is correlated with a depressed head and the length of the free 

 opercular sleeve (Gosline 1973). In ageneiosids, however, the opercular flaps are 

 fused to the isthmus well behind the center of the throat, thus contradicting any 

 correlation with the length of the free sleeve. An increase in the number of 

 branchiostegals has undoubtedly evolved independently in many lineages of 

 catfishes. Nevertheless, within any ingroup an increase in the number of 

 branchiostegals may be used to infer phylogenetic relationships (Lundberg 1982). 

 Thus, I consider this character state to be synapomorphic in those species of 

 ageneiosids with relatively high branchiostegal counts. 



The ossification pattern of the gill arches in ageneiosids is similar to that of 

 ictalurids and many other catfishes (Lundberg 1982). Only the second and third 

 basibranchials are ossified. The first two hypobranchials are ossified and obliquely 

 concave on their anterior margins, and have the medial cartilaginous flanges 

 situated anterior to the lateral edges of the bones (Fig. 12). Ferraris (1988) found 

 that this structure and arrangement of the first two hypobranchials was unique to 

 ageneiosids. All five ceratobranchials are ossified, and the fifth pair are expanded 

 to support large pharyngeal tooth plates, each bearing a large number of moderately 

 strong teeth. The ceratobranchials bear the majority of the gill rakers on each arch. 

 All five epibranchials are ossified and bear gill rakers in two rows. There is a pair of 

 large oval pharyngeal tooth plates supported by the infrapharyngobranchials and 





