A new Subfamily Dirimiinae of the Family Kumpanophyllidae Fomichev, 1953 is introduced on the basis of Dirimia gen. nov., which is represented by six new named species and three species left in open nomenclature. The new species are Dirimia multiplexa, D. similis, D. recessia, D. composita, D. extrema, D. nana, Dirimia sp. 1, Dirimia sp. 2 and Dirimia sp. 3. The progressing atrophy of the columnotheca, leading to its total reduction in extreme species, and the occurrence of an axial structure instead of a compact pseudocolumella established in these species are accepted as differences exceeding the genus level. All specimens assigned to this subfamily were derived from the same Limestone F1 of the Donets Basin, and mostly from the same locality. The reasons for their split into a relatively large number of species are: 1) an increased radiation typical for faunal turnover times; 2) a delay in the appearance of differentiated skeletal characters relative to the appearance of genetic differences large enough to characterise different species; 3) a bias in preservation of fossil remnants by comparison to living populations, amplified by biases in the collections available for study by comparison to the total number of specimens fossilised.
