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We here describe Liodessus lacunaviridissp. n. (Coleoptera: Dytiscidae, Bidessini), collected from small mossy puddles at the edge of the Laguna Verde, Boyaca, Colombia. Within LiodessusGuignot, 1939 the new species is well characted by its darker coloration, more elongate oval habitus, and the shape of the median lobe in ventral view, which is more evenly narrowing than in the other Andean species known so far. In addition to external morphology, we used mitochondrial cox1sequence data to support the generic assignment and delineate the new species. Altogether 32 species of the genus are now known from the Americas, 12 of them from the Andean region.

Laccophilus bapakn. sp., L. ekarin. sp., L. papuanusn. sp. and L. ramuensisn. sp. are described from New Guinea. The sister-species of L. bapakis L. seminigerFauvel 1883, whereas L. papuanusis close to L. univittatusRégimbart 1891. L. ekariand L. ramuensisare both close to L. transversalisRégimbart 1877. There is strong evidence that many species-groups of LaccophilusLeach 1815 as currently delimited are paraphyletic, and features supporting this hypothesis are briefly discussed. Apically bifid metatibial spurs are an apomorphy of the genus Laccophilus, thus the acute spurs in L. bapakare interpreted as a character reversal according to the cladistic analysis carried out here. Recent New Guinea localities are listed for all the Laccophilusspecies. Features for the identification of L. seminigerand L. univittatusare also given. Twelve species of Laccophilusare known at present from New Guinea, but the report of four additional species by GUEORGUIEV & ROCCHI 1993 (L. decoratusBoheman 1858, L. parvulusAubé 1838, L. sharpiRégimbart 1889, and L. ritsemaeRégimbart 1880) requires confirmation. The distribution ranges of all New Guinea species are summarized on maps. We also found evidence that PhilodytesBalfour-Browne 1939 cannot be a valid genus but is a subgenus of Laccophilusand the occurrence of acute metatibial spurs in its only species, L. umbrinusMotschulsky 1859 is due to reversal. An unusually high proportion of the dytiscid fanua of New Guinea, including Laccophilusspecies, is composed of dark or melanistic forms. It is postulated that the shading of the lentic habitats by the luxuriant vegetation favours the occurrence of dark coloured water beetles.