The genus Cyrtosomum was erected by Gedoelst (1919) to receive an atractid nematode from a North and Central American iguanid, Sceloporus undulatus (Daudin). The name proposed for the new species was Cyrtosomumt scelopori Gedoelst, 1919. Bravo-Hollis (1942) redescribed C. scelopori from another host, Ctenosaura acanthura (Shaw), a large herbivorus iguanid of Mexico. Recently, the present author obtained specimens, which have been identified by the author as C. scelopori, from 3 other large herbivorus iguanids. Two of these are native to the southwestern deserts of the United States, Dipsosaurus d. dorsalis (Baird and Girard) and Sauromalus obesus (Baird). The third, Ctenosaura hemilopha (Cope), is found in Mexico.