This is a small genus that appears to be concentrated around Central Asia though some species are holarctic. There are now 5 species that occur in Britain. Benson considered Eutomostethus nigrans to be a variation of ephippium.
The genus is characterised by the presence of a prepectus as a raised rim to the front edge of the mesepisternum, separated by a rough deep sulcus. The anal cell of the forewing lacks a coss-vein and the basal anal vein A3 of the forewing is curved back towards veins A1 and A2. The antennae are short with the third antennal segment shorter than the sum of the apical 3 segments.
All 5 species are associated with grasses, sedges and rushes.
Eutomostethus ephippium (Panzer, 1798)
Eutomostethus gagathinus (Klug, 1816)
Eutomostethus luteiventris (Klug, 1816)
Eutomostethus nigrans (Konow, 1887)
Eutomostethus punctatus (Konow, 1887)
Benson, R.B., 1952. Handbooks for the Identification of British Insects. Hymenoptera, Symphyta, Vol 6, Section 2(a-c), Royal Entomological Society, London
Liston A, Knight G, Sheppard D, Broad G, Livermore L (2014) Checklist of British and Irish Hymenoptera - Sawflies, ‘Symphyta’. Biodiversity Data Journal 2: e1168. https://doi.org/10.3897/BDJ.2.e1168
Macek, J. 2014: Descriptions of larvae of the Central European Eutomostethus species (Hymenoptera: Symphyta: Tenthredinidae). - Acta entomologica Musei Nationalis Pragae, Praha 54(2): 685-692
Vikberg, V, Vårdal, H, Lønnve, O. J. 2011: The occurrence of Eutomostethus ephippium (Panzer) and E. nigrans (Konow) (Hymenoptera: Symphyta: Tenthredinidae) in Northern Europe. - Sahlbergia, Helsingfors 17(1)