Trilobites belonging to the Homalonotidae are well represented in the Silurian and Early Devonian of south-eastern Australia and New Zealand, and are a significant component of the family world-wide. Their description provides an opportunity to review relationships between species and higher order taxa. A new genus Wenndorfia and two new subgenera Trimerus (Ramiotis) and T. (Edgillia) are described, and revised diagnoses are given for Trimerus, Homalonotus, Dipleura, Digonus and Parahomalonotus. Species described or redescribed from central Victoria include Homalonotus williamsi sp. nov., H. talenti sp. nov., Dipleura garratti sp. nov., Digonus wenndorfi sp. nov., Trimerus (Trimerus) vomer (Chapman, 1912), T. (T.) harrisoni (McCoy, 1876), T. (Edgillia) kinglakensis (Gill, 1949), T. (E.) jelli sp. nov., T. (Ramiotis) rickardsi sp. nov., T. (R.) tomczykowa sp. nov., T. (R.) otisi sp. nov., T. (R.) thomasi sp. nov. and Wenndorfia lilydalensis (Gill, 1949). Tasmanian species described include T. (R.) iani sp. nov., Brongniartella? sp. and D. zeehanensis (Gill, 1949). Wenndorfia expansa (Hector, 1876) (= H. (Burmeisteria) huttoni Allan, 1935, = D. margaritifer Wenndorf, 1990) from New Zealand is redescribed.
Complex relationships between trilobite faunal composition and taphonomy demonstrate that homalonotid assemblages are inadequately described by the biofacies concept. A recurrent relationship can be recognised between homalonotid-dominated low diversity assemblages and high diversity assemblages in relatively shallower-water facies in which homalonotids are minor faunal elements. These paired assemblages occur variously along a bathymetric gradient that reflects specific environmental tolerances, and precludes the definition of discrete assemblage-facies associations.
Keywords: Trilobita, Homalonotidae, Silurian, Devonian, Australia, New Zealand, systematics, biofacies