consider the principal rays to comprise one plus the number of branched rays in 

 each lobe. However, ontogenetic variation in the branching of caudal rays, first 

 recognized in Noturus by Taylor (1969), and discussed in greater detail by Lundberg 

 and Baskin (1969) for other groups, prompted the latter authors to propose that the 

 number of lepidotrichia impinging on the primary hypural plates or muscle 

 insertions might provide more reliable comparative data among taxa. Arratia (1987, 

 partially based on earlier studies) found that procurrent rays became progressively 

 segmented during ontogeny in Nematogenys, and she suggested that comparisons of 

 segmented, unbranched caudal rays in young and adults could provide valuable 

 information for inferring phylogenetic relationships among siluroids. Despite 

 suggestions of the above authors, most recent studies have included caudal fin-ray 

 counts based on branched rays in adults. 



The ageneiosid caudal skeleton has the parhypural fused with the lower 

 plate, formed by the coalesced first and second hypurals (Fig. 30). The hemal spine 

 of the second preural typically has a laminar anterior keel along its proximal two- 

 thirds. The upper hypural plate consists of fused third and fourth hypurals. The 

 fifth hypural is separate from the remaining elements, but is closely adjoined to the 

 upper hypural plate, formed by fused third and fourth hypurals. The thin, rod-like 

 uroneural closely abuts the dorsoanterior margin of the fifth hypural. A second ural 

 centrum in not evident in adults. There is a single epural. The uppermost principal 

 ray articulates basally with the top edge of the fifth hypural. In forked-tailed 

 species, the lowermost principal ray crosses the bottom edge of the fused first 

 hypural and articulates basally with the hemal spine of the second preural; in 

 emarginate-tailed species, the lower principal ray subtends the first hypural and 

 impinges directly on the second preural hemal spine. - 



In immature specimens, the plates formed by the fused first plus second and 

 third plus fourth hypurals often have an ovoid, incompletely ossified, partially 

 cartilaginous area near the center. In larger specimens these areas are replaced by 



