The systematics and affinities of species that have previously been assigned to the terebratelloid brachiopod genus Stethothyris Thomson, 1918, are reappraised and the taxonomic composition of the Subfamily Stethothyridinae is re-evaluated. Only the type species (S. uttleyi) is retained within the genus Stethothyris. The remainder are now distributed among the new genera, Erihadrosia (E. epsilon) from New Zealand, and Epacrothyris (E. pectoralis, E. sufflata) from Australia, and Aliquantula Richardson, 1991 (A. insolita, A. tapirina). One new species (Epacrothyris rennisonae) from the Abel Head Formation, Northwest Nelson, New Zealand, is described. All but Erihadrosia are included in the Subfamily Stethothyridinae. Six other related teloform loop-bearing genera, which are also assigned to the Subfamily Stethothyridinae, are redescribed. These are Austrothyris Allan, 1939, Cudmorella Allan, 1939, Elderra Richardson, 1991, Pilkena Richardson, 1991, and Rhizothyris Thomson, 1915. The Paleocene to early Eocene (Teurian-Waipawan) species Campages chathamensis Allan, 1932 is assigned to a new genus, Tioriorithyris, which is considered the likely basal stock from which later Stethothyridinae evolved.