 Further populations were not found for several years, but were later discovered at a variety of locations, including "the bog-water on top of Swampy Hill, near Dunedin", Otautau (together with "P. subterraneus"), Ruapuke Island, Drummond, and near Invercargill.Unlike "P. subterraneus", "P. caeruleus" is a deep blue colour, which it retains even after prolonged preservation.Chilton concluded that "P. caeruleus" was the form from which "P. subterraneus" evolved.