Steindachner and A. rondoni Miranda-Ribeiro, and that the latter two species could 

 be allocated to Tympanopleura, but they did not present their rationale for this 

 conclusion. ■ l • . • . "^ 



No other species of Tympanopleura have been described and most studies 

 subsequent to the original descriptions accepted the genus as valid (e.g., Fowler 

 1945, 1951, GosUne 1945, Ortega and Vari 1986). However, Britski (1972) chose 

 not to recognize Tympanopleura, based on interspecific and ontogenetic variation of 

 the swimbladder in several species, although his conclusions were never published. 

 Based on examination of limited material of T. nigricollis, Ferraris (1988) 

 hypothesized that the three species described in Tympanopleura do not share 

 derived characters defining a more restricted clade of Ageneiosus, and hence do not 

 constitute a natural group that warrants separate generic status. For the reasons 

 detailed below, I regard the nominal genus Tympanopleura as an unnatural taxon 

 and consider the name to be a junior subjective synonym of Ageneiosus. 



As noted by Britski (1972), there are significant interspecific differences in 

 the degree of swimbladder encapsulation among ageneiosids, as well as ontogenetic 

 variation in those species with encapsulated swimbladders in adults. I found no 

 complete developmental series of any species within the material examined during 

 this study, and, in fact, there are relatively few juvenile specimens available in 

 museum collections. Nonetheless, my observations corroborate those of Britski 

 (1972). Juveniles of all species for which material was available have comparatively 

 large swimbladders, as revealed through radiographs and in counterstained 

 specimens. In some species (e.g., T. quadrifilis,A. atronasus,A.piperatus,A. brevis), 

 the swimbladder remains large and unencapsulated throughout life. In other species 

 (e.g., A. brevifilis,A. ucayalensis,A.pardalis,A. valenciennesi), there is a gradual 

 reduction and ossification of the swimbladder during growth, typically culminating 

 in maximal reduction at sizes greater than about 100 mm SL in most species. For 



