Mesothymbris Evans, 1956

Lambkin, Kevin J., 2019, Revision of Mesothymbris Evans, 1956, from the Late Triassic of Mount Crosby, Queensland (Hemiptera: Cicadomorpha: Hylicelloidea: Hylicellidae), Zootaxa 4629 (3), pp. 389-396 : 390-391

Mesothymbris Evans, 1956

Mesothymbris Evans, 1956: 191 .

Type species. Mesothymbris perkinsi Evans, 1956 , by original designation.

Triassoscytina Evans, 1956: 179 . Syn. nov.

Type species. Triassoscytina incompleta Evans, 1956 , by original designation.

(in part) Triassoscytinopsis Evans, 1956: 190 . Syn. nov.

Type species. Triassoscytinopsis stenulata Evans, 1956 , by original designation.

Emended diagnosis. Tegmen c. 3 times longer than wide, costal margin broadly convex proximally, almost straight distally, apex quite bluntly rounded; precostal carina broad at base, thence tapering to very narrow distally; marginal membrane narrow; costal space 2 times as wide as medial cell; clavus punctate, basal costal space possibly weakly punctate, tegmen otherwise smooth; point of separation of R and M at apex of basal cell noticeably kinked; basal cell long, narrow, parallel-sided, presumably closed apically by a very short arculus (not clearly preserved in any specimen); R fork quite distal, just before level of M fork; RA angled posteriorly at point of separation of RA 1, with RA 2 directed towards the apex of the tegmen; RA 1 upright, at almost 90˚to costal margin; RA 2 with 3 or 4 branches; RP simple; one ir, at ½ length of RP; one r-m, at same level as, or slightly proximal to ir, at about ½ length of M 1+2; M with 4 branches, M 1+2 fork distal to that of M 3+4; one im, between M 1+2 and M 3; M 1+2 evenly forked, M 3 deflected at im; intra-medial cell short and quite broad, c. 3 times longer than wide, deflected towards CuA at m-cua which is at ½ length of M 3+4; CuA just distal to basal cell strongly curved and very closely approximating claval suture; CuA fork quite shallow, at about level of apex of clavus, well beyond level of M fork; m-cua between M 3+4 and CuA.

Notes. Evans originally placed all three genera in the Scytinopteridae , an attribution supported by Bekker- Migdisova (1962), Carpenter (1992 – although also noting Triassoscytina as “Family position uncertain”) and Martins-Neto et al. (2003) (but as Scytinopteromorpha). Later Evans (1964) considered Mesothymbris and Triassoscytinopsis as cicadelloids, whereas Jell (2004) retained Triassoscytina and Triassoscytinopsis in the Scytinopteridae , but ascribed Mesothymbris to the Cicadellidae . Notwithstanding the fact that the definition, generic composition and classification of the Hylicellidae remain unresolved, the attribution of the three genera to the family by Hamilton (1992) is supported herein. Shcherbakov (1988, 2012) proposed a division of the Hylicellidae into three subfamilies: Hylicellinae Evans, 1956, based on the genotype Hylicella Evans, 1956 ; Vietocylinae Shcherbakov, 1988, comprising Cycloscytina Martynov, 1926 , and Vietocycla Shcherbakov, 1988 , with a tegmen diagnosis of “basal cell closed by point of anastomosis, several post-nodal branches of R, no less than two r-m and four of M” ( Shcherbakov 1988); and Conjucellinae Shcherbakov, 2012, comprising Conjucella Shcherbakov, 2012 , Cinemala Shcherbakov, 2012 , Homopterites Handlirsch, 1906 , and Liassocercopis Ansorge, 1996 , with a tegmen differing from other hylicellids in “the poor vein branching, absence of arcular fold, trait to align arculus with CuA base, and medial cell small and/or contiguous with radial cell and/or CuA fork” ( Shcherbakov 2012). The tegmen of Mesothymbris does not conform with the above diagnoses nor the published illustrations of the tegmina of the genera of the Vietocyclinae or Conjucellinae. The third subfamily, Hylicellinae, lacks clear definition, and so at this stage Mesothymbris can only be designated as Hylicellidae incertae sedis. It is, however, clearly distinct from the other Mount Crosby hylicellids, Hylicella and Triassocotis Evans, 1956 (the position of Triassoscelis Evans, 1956 , based only on the apical half of the tegmen, remains unclear) in the quite distal forking of R, just before that of M (much more proximal in the other two genera); the distinct angle in RA at the point of separation of RA 1, with RA 2 directed apically (in the other two genera RA not angled, with RA 2 continuing antero-apically); the upright RA 1 (inclined in the other two genera); the quite broad intra-medial cell, c. 3 times longer than wide (even broader in Hylicella , c. 2 times longer than wide, but much narrower in Triassocotis , c. 4 times longer than wide); M 3+4 separate from CuA 1 (M 3+4 and CuA 1 fused for a short length in Hylicella , therefore no m-cua); m-cua at about ½ length of M 3+4 and running to CuA (at about ¼ length of M 3+4, and running to CuA 1 in Triassocotis ); CuA just beyond the basal cell strongly curved and closely approximating the claval suture (gently curved and more distant in the other two genera); and in the shallow fork of CuA (similar in Hylicella , much deeper in Triassocotis , at about same level as that of M, and well before the apex of the clavus).

Evans (1956) ascribed three species to his Triassoscytinopsis , the type species and T. aberrans Evans , both from Mount Crosby, and T. paranotalis Evans from the Triassic of Brookvale, New South Wales. Both the type species and T. aberrans are synonyms of the type species of Mesothymbris , however, T. paranotalis , apparently with an inclined RA 1 and three inter-radial crossveins ( Evans 1956, fig. 5A), almost certainly belongs elsewhere.