Five new species of pharyngodonid (Oxyuroidea) nematodies are described from the posterior gut of A. yemenensis (Agamidae) in Saudi Arabia as follows: Tachygonetria paradentata sp. nov., a member of the ''T. dentata'' complex, mostly closely resembles T. quentini Petter, 1966 from Testudo tentoria verreauxi from South Africa in the form and disposition of cephalic sense organs; it is distinguished by having caudal alae, an anterior anal lip in the male formed by 2 sharply-elbowed lobes and by the fact that the terminal spine on the caudal appendage of the male is much shorter than that in Tachygonetria quentini. Alaeuris asirensis sp. nov. is most similar to a species described as Thelandros sexlabiata Ortlepp. 1933 from Testudo tenoria verreauxi from South Africa: the last pair of caudal papillae in the male is subterminal; there are 6 lips and a slight prevulvar swelling in the female. Males of the 2 spp. are easily distinguished by the presence of caudal alae and a longer caudal appendage in A. asirensis females are distinguished by the fact that lips are less developed in the new species. The fact that 2 such similar species cannot be included in the same genus reflects the need for a redefinition of Alaeuris. Thelandros agama sp. nov. resembles T. alatus Wedl, 1862 from Uromastix sp. in North Africa in the cephalic structure of the female and in the shape of the peduncles supporting adanal papillae in males; the new species is distinguished by its longer spicule and by the presence of caudal alae and the absence of lips in males. T. masaae sp. nov. resembles T. taylori Chatterji, 1935 and T. baylisi Chatterji, 1935 from Agama sp. and Uromastix sp. in India in that the peduncles supporting the caudal papillae in the male are elongate; it differs from both and from all other members of the genus in that the vulva is located at the end of a long tube-like exvagination of the body wall and the anterior anal lip of the male is simple rather than fringed. T. petterae sp. nov. resembles T. taylori and T. baylisi in having well-developed caudal alae in males and 6 prominent lips in females; it is distinguished fom both by its flask-shaped adanal peduncles in the male. Thelandros is redefined to include only those species in which the pre- and adanal papillae are pedunculate and the opening to the spicular pouch is markedly postanal. The 9 genera of the Pharyngodonidae in herbivorous and omnivorous reptiles form an evolutionary line distinct from that in insectivorous reptiles. This line probably arose in tortoises in Laurasia in the Eocene, spread with these hosts to Africa, Madagascar and South America, and subsequently underwent evolutionary radiations in each of these regions. Pharyngodonids of A. yemenensis have a double origin: the thelandros spp. probably evolved with agamids; species of Tachygonetria and Alaeuris are likely captures from tortoises.
