

shaped occipital-nuchal region posteriorly (Figs. 3-6). The general shape in dorsal 

 profile varies little among species. Many of the elements are extremely porous, 

 especially in small species and juveniles of larger species. The surface texture of the 

 bones is weakly rugose or ridged. The cancellous nature of cranial bones was 

 considered by Stewart (1986) to be a derived condition, and it has apparently 

 evolved independently m some pimelodids, Hypophthalmus, and ageneiosids. 

 Cranial bones are relatively nonporous in the auchenipterid genera that I have 

 examined, and most doradoids have extremely solid cranial bones; thus, I consider 

 the poor ossification of skull bones in ageneiosids to be uniquely derived among 

 doradoids. Ageneiosids also have porous bones in other parts of the body, 

 especially the basipterygia and the caudal skeleton. Cancellous bones and a high 

 body-fat content in ageneiosids and Hypophthalmus may be involved in maintaining 

 neutral or positive buoyancy (Howes 1983). 



The nasal bones are thin, tubular, and bifurcated at their midline. The 

 forked nasal was thought by Ferraris (1988) to be a synapomorphy of ageneiosids. 

 In all other catfishes, the nasal is penetrated by three foramina for the supraorbital 

 sensory canal (Lundberg 1982). The main portion of the canal passes through the 

 anterior and posterior foramina, but a second branch passes through an 

 anterolateral foramen to the second supraorbital pore. In ageneiosids, the proximal 

 portion of the lateral canal is ossified by cancellous bone. -, 



The mesethmoid bears broad lateral comua, as in the majority of catfishes 

 (Lundberg 1982). The front margin has a relatively shallow median cleft (Figs. 3-6). 

 Anteroventrally, the mesethmoid supports the premaxillae, which are broadly 

 expanded mesially, and gently to strongly curved laterally, depending on the species. 

 The premaxillae are heavily toothed over their entire ventral surface with relatively 

 short, sharp, recurved teeth (further described under oromandibular region). 



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