Members of the genus Linognathoides are ectoparasites of ground squirrels and marmots (Rodentia: Sciuridae) in the Nearctic, Palearctic, and Afrotropical regions. Linognathoides urocitelli n. sp. is described based on adult male and female and third-instar nymphal specimens collected from the long-tailed ground squirrel (Urocitellus undulatus) in Mongolia. The new species is compared morphologically to other members of the genus Linognathoides. Additionally, DNA sequences of a 610–base pair (bp) fragment of the nuclear 18S rDNA gene, a 452-bp fragment of the mitochondrial 12S rrnS gene, and a 363-bp fragment of the mitochondrial 16S rrnL gene are provided. Host associations and geographical distributions of the 11 previously recognized species of the genus, and of Linognathoides urocitelli n. sp., are reviewed. A dichotomous identification key to adults of all known species in the genus Linognathoides is provided.