Subgenus † Mesohelophorus Ponomarenko, 1977 stat. nov. Mesohelophorus Ponomarenko, 1977b: 113. Type species. Mesohelophorus sibiricus Ponomarenko, 1977 (= H. palaeosibiricus nom. nov.) (by original designation). Time range. Early Cretaceous, Berriasian – Hauterivian, ca. 146–135 mya. Diagnosis. Adult: Body rather wide; mentum ca. as wide as long; gula constricted, gular sutures joint at a point; maxillary palpomere 4 symmetrical; pronotum with three longitudinal furrows; pronotal intervals bearing very distinct granulation; pronotal flanks narrow; elytron with rather long scutellar stria; alternate elytral intervals not elevated or costate; epipleuron well-developed, wide anteriorly. By the rather wide body, strongly granulate pronotum, constricted gula and symmetrical maxillary palpomere 4, Mesohelophorus resembles the species of the modern subgenera Empleurus Hope, 1838, Transithelophorus Angus, 1970, Eutrichelophorus Sharp, 1915 and Kyphohelophorus Kuwert, 1886. It may be easily distinguished from them by the presence of only three pronotal furrows (five in the modern subgenera), elytra without elevated alternate intervals or tubercles (elevated in Empleurus, Transithelophorus and Eutrichelophorus, bearing tubercles in Kyphohelophorus) and wide elytral epipleura (extremely narrow in modern taxa). In addition, it differs from Empleurus by narrow pronotal flanks (very wide in Empleurus). Mesohelophorus also resembles the modern H. (Orphelophorus) arcticus Brown, 1937 by the reduced number of pronotal grooves and strong pronotal granulation, but may be easily distinguished from it by the rather long scutellar stria on the elytron (the scutellary stria is absent, or very rarely consists of one or two punctures only in H. arcticus). Taxonomic note. Due to the presence of all diagnostic characters of Helophorus, we downgrade Mesohelophorus to a subgenus of Helophorus which seems to be confined to the early Cretaceous only. Three species of Mesohelophorus have been described till now, of which only M. palaeosibiricus nom. nov. belongs to the subgenus. Mesohelophorus elongatus is synonymised with Helophorus (Mesosperchus) tarsalis above, and Mesohelophorus mongolicus Ponomarenko, 1986 is transferred to the Buprestoidea below.

Published as part of Fikáček, Martin, Prokin, Alexander, Angus, Robert B., Pono, Alexander, Marenko, Yue, Yanli, Ren, Dong & Prokop, Jakub, 2012, Revision of Mesozoic fossils of the helophorid lineage of the superfamily Hydrophiloidea (Coleoptera: Polyphaga), pp. 89-127 in Acta Entomologica Musei Nationalis Pragae 52 (1) on page 109, DOI: 10.5281/zenodo.5330604