On the identity of Arius oncinus R. H. Schomburgk (Pisces, Nematognathi, Auchenipteridae)

The catfish which R. H. Schomburgk (1841b: 173, pl. 4) named Arius oncinus *), from a description and a drawing made in the field, has remained a puzzle to ichthyologists ever since. It is true that it has been recognized that Arius oncinus is not an Arius but belongs to the Auchenipteridae. Günther (1864: 194) merely listed the name in a footnote under Auchenipterus, without being able to do anything with it. Eigenmann & Eigenmann (1890: 266) referred to it as a "doubtful species of Centromochlus". Gosline (1945: 10) included it without comment in the genus Centromochlus under the name C. oncinus, but the only reference given is to the Eigenmanns and in the absence of material the name remained as problematic as ever. Fowler (1951) made no mention of Arius oncinus at all, probably because he found it too doubtful a species for inclusion in his work on Brazilian freshwater fishes. Finally Mees (1974: 59 footnote) quoted R. Schomburgk (1848) to show that R. H. Schomburgk's (1841b) description might be incorrect and expressed as his opinion that, whatever it was, the fish as described was not well-placed in the genera Tatia and Centromochlus. In summary it may be said that since its description no ichthyologist has known what to do with Arius oncinus and that no material was known to exist. It was therefore with considerable interest that in an illustrated article recently published (Brittan, 1976) I noted some colour photographs of a live catfish, under the name Centromochlus altae, which immediately reminded me of Schomburgk's plate f Arius oncinus. There was a reference to an earlier paper (Brittan, 1974), with another coloured plate. Correspondence with Professor Brittan revealed the presence of preserved material of this