The genus Mormyrus Linnaeus, 1758 has been well studied in western Africa where five species are currently recognized. Mormyrus subundulatus was described in 1989, and, although morphologically and genetically close to Mormyrus rume Valenciennes, 1847, is still considered by the most recent studies as a distinct species. It is endemic to the Côte d'Ivoire and Ghana River systems. It was historically recorded from only three locations but is today very likely extirpated from one of them and threatened in the remaining two. It is categorized as “Vulnerable B1ab(iii)” by the IUCN Red List (). Although a few papers describe precisely the morphology and electric signal of the species, they are based on a very limited number of samples. In this paper, we present new data on the morphological characteristics of the species (extending the dorsal fin rays count range, which is the main morphometric criterium to distinguish M. subundulatus and M. rume) based on Museum samples and samples collected recently a few kilometers away from the type locality. Determination of the newly collected material was confirmed by the analysis of a fragment of the Cytochrome b gene, and we produced the first sequence fragment of the cytochrome oxydase subunit 1 (COI) for this species.