The Cambrian trilobite 'Rhyssometopus', with taxonomic revision of Guzhangian species from Queensland, Australia

A morphometric (bivariate) analysis of middle Cambrian (Series 3; Guzhangian) species of the trilobite 'Rhyssometopus' from north-western Queensland is conducted. Results show that the species 'Rhyssometopus rhyssometopus' Öpik, 1967, 'R. princeps' Öpik, 1967, 'R. rugiceps' Öpik, 1967, and 'R. neuter' Öpik, 1967 cannot be differentiated on the basis of linear dimensions previously used by Öpik (1967) as diagnostic characters. Nonlinear characters are found to be more reliable for differentiating the species of 'Rhyssometopus'. The type species, 'R. rhyssometopus', is herein considered a senior subjective synonym of 'R. princeps' and 'R. rugiceps'. The erection of the subgenus 'Rostrifinis' is also found to be unwarranted. The occurrence of all 'Rhyssometopus' species from Australia, Antarctica and China is reviewed, and a taxonomic revision provides emended diagnoses for the following valid species: 'R. rhyssometopus' Öpik, 1967, 'R. neuter' Öpik, 1967, 'R. nitidus' Duan, 2004, 'R. rostrifinis' Öpik, 1967, 'R. thielei' (Chapman, 1911), and 'R. zhongguoensis' Zhou, 1977. The family Rhyssometopidae is also discussed, with membership consisting of the following genera: 'Rhyssometopus', 'Plectrifer', 'Qiandongaspis' and 'Tasmana'.