This particular paragraph in page 57 on Rico's suggested document may point to the question:
" The initial distinction between Melanochromis and Pseudotropheus relating to the size and configuration of the pharyngeal teeth (Trewavas 1935) is no longer considered a diagnostic feature—in fact, no distinction could be found between the pharyngeal jaws of the type species of either genus (Trewavas 1984). Another characteristic, relating to the arrangement of the oral teeth in U-shaped bands and extended on each side by a single row of unicuspid teeth (Trewavas 1984), is shared with many members of Pseudotropheus and has thus no diagnostic value. It was stated as a characteristic of Melanochromis by Trewavas (1984) but never specifically considered as a diagnostic feature. We regard the basic melanin pattern one of the important characteristics in classifying Malaŵi cichlids, and species of Melanochromis have a unique pattern that is—incomplete in some—reversed in adult males. Since the inception of the genus many workers have suggested alternative classifications for its members (Table 5), and over time the diagnosis has been enhanced and refined, but, currently, we still regard both Melanochromis and Pseudotropheus as polyphyletic. "