A monotypic genus of a new family of Merostomoidea is described from the Middle Triassic of Brookvale, New South Wales, Australia. The known range of the subclass, previously recorded from the Middle Cambrian, is extended considerably by this record.
Three well preserved non-insect arthropod specimens, apart from the xiphosuron, Austrolimulus ftetcheri Riek, (1955), have been collected from the Middle Triassic freshwater sediments at Brookvale, New South Wales. These sediments also contain abundant insects and fish. These three specimens bear a considerable resemblance in body shape to both the Synziphosurina (Merostomata) and the Merostomoidea (Trilobitomorpha). The post-cephalic portion of the body is divided into two distinct regions and ends in a long caudal style. Although appendages are not clearly preserved, their general structure can be distinguished below the crumpled pleural regions in one of the specimens and their bases distinguished in another. These numerous pairs of similar appendages are of trilobitomorph form.
Trilobitomorpha, which are first recorded from the Lower Cambrian, are not known from strata younger than the Middle Permian and almost all the species occurring since the Cambrian are referred to the well-known trilobites (Class Trilobita). The Class Trilobitoidea is, however, recorded from the Devonian as well as from the Cambrian. If these Middle Triassic specimens do belong to the Trilobitoidea they extend the known range of the class very considerably. There seems little doubt from a study of the insect remains that the sediments in which these specimens occur are of Triassic, very probably Middle Triassic, age. Etc.