A taxonomic synopsis and identification key to the genera of the Myaptex group (Diptera, Asilidae, Asilinae), with description of a remarkable new genus and three new species from the South American Chaco

<i>Cardiasilus</i> <b>gen. nov.</b> is erected to include the following three new species from Brazil and Paraguay: <i>C.aysu</i> <b>sp. nov.</b> and <i>C.dangeloi</i> <b>sp. nov.</b> (both from Mato Grosso do Sul, Brazil) and <i>C.ruda</i> <b>sp. nov.</b> (Paraguay), which are herein described and illustrated. The new genus is placed into the <i>Myaptex</i> group of the subfamily Asilinae based on the following set of characters: wing with cells <i>r₂₊₃</i> and <i>r₄</i> not separated by a recurrent vein (i.e., only two submarginal cells); costal section between tips of veins <i>R₅</i> and <i>M₁</i> much shorter than costal section between tips of <i>R₄</i> and <i>R₅</i> , with <i>R₅</i> ending bellow wing apex; scutellum tumid, with no sign of an impressed rim and with at least one pair of well-developed apical scutellar macrosetae; claws acute; and abdominal tergites with lateral marginal macrosetae. It can be differentiated from the other genera of the group by the scutum lacking anterior dorsocentral setae, male epandrium inflated (which resembles the ideogram of a heart in dorsal view), male and female sternites 2-6 with lateral macrosetae, and the male sternite 8 with a long digitiform projection at middle of posterior margin. An illustrated identification key to the genera of the <i>Myaptex</i> group, as well as to the males of <i>Cardiasilus</i> <b>gen. nov.</b>, are also provided.