where it articulates with a notch in the posttemporal (Fig. 25). The relatively long 

 horizontal limb extends obliquely forward and is broadly sutured with its antimere 

 at the midhne. The cleithrum is broadly fused to the coracoid along the entire 

 anteroventral margin. The coracoids broadly suture at the midline anterior to the 

 cleithral suture. 



There is no postcleithral process (PCP) in most ageneiosids, although a short 

 one is always present in Tetranematichthys, and it is usually present in A. brevis. All 

 other doradoids have a PCP. The primitive condition for catfishes is the presence of 

 a moderately developed, unomamented PCP (Lundberg 1982), so that loss or 

 reduction of this structure is derived in ageneiosids (Ferraris 1988). There has been 

 considerable divergence among siluriforms in the morphology of the PCP, indicating 

 parallel evolution (Lundberg 1982). Several other lineages of neotropical catfishes 

 have independently lost the process (Stewart 1986). At the other extreme, nearly all 

 doradids have a very strong, heavily ornamented PCP, which probably represents a 

 separately derived state. Stewart (1986) stated that there is a positive correlation 

 between the relative size of the PCP and strength of the pectoral-fin spine and 

 locking mechanism in pimelodids. This argument can be applied to ageneiosids, in 

 which the pectoral-fin spine is relatively weak in comparison to many other 

 catfishes. The two species in which the PCP is present have relatively robust fin 

 spines within the family. ,; , 



The ageneiosid first pectoral lepidotrichium is a relatively thin, moderately 

 serrated defensive spine in most species (Fig. 26). In A. brevifilis and A. marmoratus 

 the first pectoral ray is segmented, weakly serrated, flexible, and tapers to a thin 

 membranous tip (Fig. 26a). A somewhat intermediate condition between these two 

 species and other ageneiosids is found in A. pofystictus, in which the spine is stiff and 

 unsegmented proximally, but flexible and branched distally. A strong and heavily 

 ossified spine is primitive for catfishes; thus, the reduced strength of the spine is 

 derived in the above species. The spines of .4. atronasus,A. brevis, and 



