The postsupraocular, a small oblique scale just posterior to the supraoculars and medial to the pretemporal scales, is a derived character within the taxonomically difficult Sphenomorphus group of lygosomine skinks. This character occurs in 22 of the approximately 125 described species of Sphenomorphus currently recognized. The species with this distinctive character occur in the southern Philippine Islands, New Guinea, and the Solomon Islands and are called, informally, the Sphenomorphus maindroni group. A new species in the group is described from New Guinea, where most of the species occur. A key to the species with the distinctive character is provided.