Revision of the Hylicellidae of the Late Triassic of Queensland (Hemiptera: Cicadomorpha: Hylicelloidea)

Abstract

This extinct cicadomorphan family Hylicellidae was a significant element of the Late Triassic (Norian) hemipteran fauna of south-eastern Queensland, represented by the tegmina of five monotypic genera from the fossil insect localities at Mount Crosby, Denmark Hill and Dinmore. Of the five, Mesothymbris Evans, 1956, from Mount Crosby, has previously been re-examined. The present work revises the remaining four genera: Hylicella Evans, 1956, with Hylicella colorata Evans, 1956, Mount Crosby; Crosbella Evans, 1956 (= Mesocicadella Evans, 1956, syn. nov.), with Crosbella elongata Evans, 1956 (= Crosbella alata Evans, 1956, syn. nov. = Mesocicadella venosa Evans, 1956, syn. nov. = Mesocicadella punctata Evans, 1961, syn. nov.), Mount Crosby; Triassoscelis Evans, 1956, with Triassoscelis anomala Evans, 1956, Mount Crosby; and Mesocixiodes Tillyard, 1922, with Mesocixiodes termioneura Tillyard, 1922 (= Mesocixiodes brachyclada Tillyard, 1922, syn. nov.), Denmark Hill, Dinmore. The Hylicellidae remains poorly defined as is its generic composition, however, the four Queensland Triassic genera are quite distinct. Hylicella is distinguished by the partial fusion of CuA₁ with M₃₊₄, and the very large intra-medial cell, and Crosbella and Triassoscelis by the peculiar parallelogram-like CuA₁ cell and the widened peripheral membrane at CuA. Triassoscelis differs from Crosbella in its broader, more squat wing shape, CuA fork in line rather than proximal to the M fork, and much less proliferated apical venation. Mesocixiodes is distinguished by the alignment of the crossvein field at the claval apex to form a fairly even series of long, sub-equal apical cells. On the basis of the proliferated and variable apical venation, the presence of weakly developed costal veinlets, and the fusion of M and CuA at a single point to close the basal cell, Crosbella and Triassoscelis, are ascribed to the subfamily Vietocyclinae. The relationships of the three other Queensland genera, Hylicella, Mesocixiodes, and Mesothymbris remain obscure, and they are retained in the undefined catch-all subfamily Hylicellinae. With the exception of the hindwing, Mesojassula marginata Evans, 1956, the revision of the cicadomorphan fauna of the Mount Crosby Formation is now complete, resulting in an inventory of five species of Dysmorphoptilidae, four of Hylicellidae and two of Archijassidae, with the dysmorphoptilid Dysmorphoptiloides elongata Evans, 1956, as the dominant species.