Pericoptus populations which live in dry inland sand dunes and sandy patches within or adjacent to the beds of the southern braided rivers, the Clutha, Wairau, Waiau, Waimakariri, Rakaia, Rangitata, and similar habitats in the Mackenzie Basin are referred to a separate species P. frontalis. These inland populations have not been studied and may represent further species. Some may well be now non-existant and putative species could be extinct. These inland populations/species are shown here as one species.
P. frontalis and its distant relative Prodontria lewisi of the Cromwell Beetle Reserve (Clutha River terrace) are now endangered by the depredations of the Australian red-back spider . The other riverine populations are restricted by the invasion by weedy plants - gorse, Russell lupin and many less obvious pests.