The early Permian (Asselian-Sakmarian) Lyons Group consisting of tillite, greywacke, sandstone, siltstone, and conglomerate rests unconformably on the Precambrian basement and is conformably overlain by the Permian (Artinskian) Callytharra Formation. Bryozoa occur in thin, local, calcareous lenses in the Lyons Group, 4,600 feet thick in its type section, whereas they form rich bryozoan calcarenites and bryozoan calcirudites in the overlying Callytharra Formation, 765 feet thick. The stenoporid species in the Lyons Group display similarities to certain Eastern Australian forms from the early Permian, and a well distributed fenestellid species of Polypora has close affinities with species from the Lower Permian in Eastern Australia and from the Bitauni Beds (equivalent to t e Asselian Series of Russia) from Timor. These species of Polypora appear to be primitive members of a well-defined phylogenetic group of species including P. tuberculifera, P. punctata, P. subovaticellata, and P. nadinae from the upper part of the Sakmarian Series of the Ural Mountains. The geographic and stratigraphic distributions of such early Permian bryozoan lineages appear useful tools in the correlation of different stratigraphic units.

The generic and specific composition of the bryozoans in the overlying Callytharra Formation is vastly different and the bryozoan faunal break between these two stratigraphic units is very distinctive. Genera such as Hexagonella, Evactinopora, Protoretepora, Ramipora, Streblotrypa, Rhombocladia, and Streblocladia which are prominent in the Callytharra bryozoan faunas are not found in the Lyons Group.

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