Billibathynella humphreysi gen. et sp. nov. is described from calcrete aquifers located in the Yilgarn Craton of north-western Australia. This is the first parabathynellid known from the Australian Precambrian shields, which have never been inundated by the sea. A comparison of the primitive species so far known from Australia and other continents points to the new species as being the most primitive among the parabathynellids. It further suggests that the new genus has an affinity to Notobathynella Schminke, but differs in having a six-segmented antenna and a large epipod of the male thoracopod VIII. An attempt to relate the primitiveness of the new species to the historiogeological characteristics of the region has led to the conclusion that the recent parabathynellids could have emerged from freshwater epigean ancestors. It is further assumed that the transition of their ancestors to groundwaters happened in Notogaea.

Three new species of the genus Hexabathynella, H. otayana sp. n., H. hessleri sp. n. and H. muliebris sp. n., from North America are described. A comparison with previous studies results in the reevaluation of characters already known and the discovery of new constitutive characters. The distal spine of the mandibular spine row is regarded as a synapomorphy of the three new species and two previously known species, H. knoepffleri, H. minuta, which constitute a monophyletic group within the genus, the knoepffleri‐group. The phylogenetic relationships between the five species are depicted with a cladogram. The setation on the uropodal exopod is shown to be not only a new unique character for the genus, but also a significant one in classifying its species. The presence of the ancestor species of the genus before the Triassic and dispersal during Mesozoic continental drift are assumed to explain the transatlantic occurrence of the knoepffleri‐group and the distribution pattern of the other species.

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The genus Hexabathynella (Crustacea, Malacostraca, Bathynellacea) is revised in the sense of the phylogenetic systematics and four new species are described from South Africa ( H. monoaethetasca sp. nov. and H. africana sp. nov. ) and America ( H. schrieveri sp. nov. and H. virginiae sp. nov. ). A comparative analysis of all observable outer structures distributed in 18 known and four new species resulted in a re-evaluation of 18 characters and character states. The phylogenetic analysis using the program PAUP yielded one most-parsimonious tree, which suggests the grouping of ( H. decora (