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[[ Genus Stomatorhinus Boulenger ZBK ]]
Stomatorhinus Boulenger 1898 ZBK is a genus of small mormyrid weakly electric fishes from African freshwaters that is diagnosed by having widely separated nares with the posterior nares located close to the mouth. In all other mormyrid genera the posterior nares are remote from the mouth. A second putative synapomorphy for the genus comes from the study of neuroanatomy: the electrosensory lateral line lobe has two distinct zones on each side of the midline in all assayed species of Stomatorhinus ZBK (7 of 12) in contrast to the three distinct zones found in all other mormyrid species examined to date (Bell & Russell 1978; McNamara, Denizot and Hopkins in press).
Twelve species of Stomatorhinus ZBK are regarded as valid (Gosse 1984). Ten of these are endemic to the Congo River basin; an eleventh is found in both the lower Congo and the coastal Chiloango River, just north of the Congo River mouth. Stomatorhinus walkeri ( Guenther 1867) , from the Ogooué and Kouilou-Nairi river basins, is the type species of the genus and the only species described from a region remote from the Congo basin to date. Here we describe a new species of Stomatorhinus ZBK known only from the Ivindo River basin in Gabon. Although the Ivindo is a large tributary of the Ogooué , there are no records of S. walkeri from it. Adults of the Ivindo basin Stomatorhinus ZBK species are significantly smaller than adults of S. walkeri and differ in body proportions, counts and coloration. Harder (2000) assigned these Ivindo basin Stomatorhinus ZBK specimens to S. fuliginosus Poll 1941 ZBK , a species described from the Congo basin to which they are more similar in counts, measurements and overall size than they are to S. walkeri . Here we show that the Stomatorhinus ZBK from the Ivindo River basin is distinct from S. fuliginosus ZBK , S. walkeri and other described Stomatorhinus ZBK and recognize it as a new species.