A monophyletic group of genera, the pachynid group, is established within the lysianassoid amphipods for genera with an extremely compressed carpus and enlarged propodus on gnathopod 1. Two subgroups within the pachynids are established for genera with smooth or with sculptured spine-teeth on maxilla 1. Four new genera—Sheardella, Drummondia, Acheronia and Ekelofia—and 10 new species—Sheardella kapala, S. tangaroa, Drummondia corinellae, D. parviramus, Pachynus pugilator, P. denticulatum, Figorella tasmanica, Acheronia pegasus, Pachychelium schellenbergi and P. nichollsi—aredescribed. A further 4 genera and 8 species are rediagnosed or redescribed. Pachychelium mediterraneum is transferred to Prachynella and Ekelofia is established for Pachychelium oculatum.