Sri Lankan species of the genus Tmarus are cryptic spiders that live either on greenish moss-covered twigs or brownish dried-out twigs. They have remained taxonomically unrevised. The only known species was misplaced in Peritraeus Simon, 1895, which has never been subjected to phylogenetic evaluation. The present study is designed to investigate the phylogenetic placement of Sri Lankan Tmarus within Thomisidae as well as to assess the validity of Peritraeus and its relationship to Tmarus and Monaeses, if any. Using a multilocus molecular dataset (16S–ND1, 28S, CO1 and H3) we provide evidence that Tmarus and Monaeses are paraphyletic and that Peritraeus is a junior subjective synonym of Tmarus. Four species of Tmarus, including three new species, are now recorded from Sri Lanka. The legacy groups Alcimochthae and Tmarae are confirmed to be polyphyletic. Further, the following new species are described: Tmarus hiyarensis, sp. nov., T. viridomaculatus, sp. nov. and T. manojkaushalyai sp. nov. The following new combination is proposed: Tmarus hystrix (Simon, 1895), comb. nov. (this results in a homonym with Tmarus hystrix Caporiacco, 1954: we rename the species Tmarus caporioccoi Ileperuma Arachchi & Benjamin, replacement name).