>* "'■ 111 



•-. ' i :■■■'- s» 



united to the bifid horns of the apex of the anterior plate, situated on either side of 

 the dorsal-fin spine (Figs. 3-6). t -/^ <^ 



Since most doradoids have three prominent nuchal plates (counting the 

 posterior pair as one), Royero (1987) and Ferraris (1988) regarded the absence of 

 the anterior plate in Ageneiosus to be a derived state. Presumably, loss of the plate 

 in Centromochlus (Ferraris 1988) is convergent with the condition in Ageneiosus, in 

 the absence of any corroborative evidence to support a close relationship between 

 these taxa. 



The remaining pterygiophores of the ageneiosid dorsal fin are much smaller 

 than the first two, similar in shape, and do not contact the vertebral column. Each 

 bears a cartilaginous bar corresponding to the medial radial, and a distal 

 cartilaginous radial lying between the bifid halves of the branched lepidotrichia 

 (Figs. 17, 24). ' ■ 



V .;■»;; Pectoral Girdle 



The siluriform pectoral skeleton has been investigated in a number of 

 phyletic studies of ostariophysan relationships and functional morphology (Regan 

 1911, Tilak 1963, Alexander 1965, Lundberg 1975, and Gosline 1977). In his 

 benchmark revision, Regan (1911) noted the highly characteristic pectoral girdle of 

 catfishes, and stated that the mesocoracoid arch was absent in the Ariidae, 

 Bunocephalidae (= Aspredinidae), and the Doradidae (including the 

 auchenipterids and ageneiosids). Absence of the mesocoracoid was repeated by 

 Ferraris (1988) as a uniform condition among doradoids. However, Diplomystes 

 lacks a well-developed mesocoracoid (Alexander 1965, Arratia 1987), suggesting 

 that its presence in some catfishes represents a derived state. 



The ageneiosid pectoral girdle is relatively generalized in comparison with 

 most other catfishes. The long vertical Umb of the cleithrum is bifurcated dorsally. 



