Genus Archaenosodendron Li & Cai gen. nov.

Type species. Nosodendron cretaceum Deng, Zhou, Ślipiński, Ren & Pang, 2018

Etymology. The generic name is composed of “ Archae- ”, ancient, and “ Nosodendron ”. The name is neuter in gender.

Diagnosis. Body elongated oval, generally less than 5 mm long. Eyes not strongly protuberant. Prosternum in front coxae not extremely shortened, longer than half length of prosternal process, with incomplete antennal grooves. Protibia expanded apically; outer edge of protibia with one row of distinct denticles. Tarsomeres slender, not distinctly lobed.

Remarks. Deng et al. (2019) originally placed N. cretaceum in the extant genus Nosodendron, since the species differs from the only other extant genus, Nosoglobulus, in having a larger body and relatively loosely articulated antennal club. They additionally noted that N. cretaceum differs from both of the extant subgenera in Nosodendron in the combination of several characters. Recently, we discovered several additional species related to N. cretaceum from Burmese amber. Based on the examination of the new materials, as well as the holotype of N. cretaceum, we suggest that the difference between this fossil group and extant Nosodendron is large enough to justify a new genus, which is herein designated as Archaenosodendron.

In extant Nosodendron (and Nosoglobulus), the prosternum in front of coxae is extremely shortened, while in Archaenosodendron the prosternum is relatively long. More importantly, in extant Nosodendron, the lateral portions of prosternum are clearly delimited and are distinctly lower compared to the medial portion (raised mesal shelf; fig. 4B in Nomura & Kamezawa 2014), so that when in repose the fore legs can fold compactly and the protrochanters and profemora could lay exactly on the lowered lateral portions of prosternum. In Archaenosodendron, although the lateral portions of prosternum might be somewhat lowered, there is no clear and complete boundary between the lateral and medial portions, and the protrochanters and profemora are unlikely to be able to lay compactly against the prosternum.

Key to species of Archaenosodendron

1. Mentum with somewhat longitudinally arranged larger punctures along the lateral margins and smaller punctures in the medial (anteromedial) region (Fig. 8B)................................................ A. explanatum Li & Cai sp. nov.

- Punctures on the mentum not forming the pattern above....................................................... 2

2. Outer edge of protibia with about 14–16 relatively sparsely arranged denticles/stout setae, with the apical two distinctly stouter and more closely situated (Fig. 11G). Medial and lateral portions of prosternum not clearly separated (Fig. 11D)..................................................................................... A. remotidens Li & Cai sp. nov.

- Outer edge of protibia with more denticles/stout setae; the apical two not forming the pattern above. Medial and lateral portions of prosternum separated by an incomplete ridge (Figs 4C, 14D)................................................. 3

3. Outer edge of protibia with about 30 densely arranged denticles (Fig. 4G–J). Mentum with anterior angles not obviously produced (Fig. 4A).................................................................. A. cretaceum (Deng et al.)

- Outer edge of protibia with about 20 denticles/stout setae (Fig. 14F–H). Mentum with anterior angles pointed anterolaterally (Fig. 14B)................................................................... A. angulare Li & Cai sp. nov.