A new species is described in the tarantula genus Lyrognathus Pocock 1895, being the first record of this taxon from Sumatra, Indonesia. Lyrognathus giannisposatoi sp. nov. is also unique in its habitat selection, being the first confirmed lowland species from this genus. A new key to Lyrognathus species is provided, and a biogeography of the group is briefly discussed. 1. Introduction Lyrognathus Pocock 1895 belongs to the tarantula subfamily Selenocosmiinae Simon 1889 and was first described in northeastern India (L. crotalus Pocock [1], L. saltator Pocock [2]), then a century later in West Malaysia (L. robustus Smith [3], West [4]), and more recently on Borneo (L. achilles West and Nunn [5], L. fuscus West and Nunn [5]) and Lombok islands (L. lessunda West and Nunn [5]). West and Nunn revised the genus [5] and in 2012 subjected Lyrognathus to cladistic analyses and also discussed biogeographical history of the group [6]. All previously described species have been recorded at higher elevations in montane habitat [1, 2, 4, 5, 7] and are a relatively medium to small-sized group [5]. Lyrognathus giannisposatoi sp. nov. is the most robust member of the genus and is the first to be recorded from Sumatra. L. giannisposatoi sp. nov. is unique among Lyrognathus in its preference for lowland elevations (F. Schneider, pers. comm.). A new key to species and map of Lyrognathus are also included. 2. Material and Methods Taxonomic description style follows Raven [8] and West and Nunn [5]. All measurements are given in millimeters (mm) and were made to the nearest 0.01？mm with the aid of a squared eyepiece and digital dial callipers. Life images were taken with a Nikon CP8800 digital camera. Taxonomic images were taken by mounting a Nikon CP8800 digital camera to the phototube of a WILD Heerbrugg M8 stereozoom microscope (plus 1.6X objective lens) via the Scopetronix Maxview TM system, with external cold light illumination. Additional images of paratypes in the SMF were taken by Wirth with a Novex RZ Range trinocular microscope and a Nikon CP4500 digital camera, with external cold light illumination. The species diagnosis defines L. giannisposatoi sp. nov. from all others within the genus, not just its closest relatives. Leg and pedipalp measurements were taken from their dorsal aspect on the left side (unless appendages were lost or obviously regenerated) of all specimens, and coxae and trochantera were measured from their ventral aspect, on the same side. Eyes in sizes of largest to smallest (including distances taken at widest points in length/width, resp.).
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