A species of mermithid nematode was found parasitizing the larvae of Culex fatigans in the region of Xinyang County, Henan Province in 1984. It was ident- ified as a new species of the genus Roraanomerrais (Nematoda:Mermithidae),named Romanoraermis yunanesis. Besides the diagnostic feature of the genus, the main characters of this new species are: Female:Boby length 21.1mm (n=36, r=14.6-28.6, SE=0.49) .Width at the vagina 164 (n=33, r = 118-212, SE=4.05) . Vagina pear shaped the midway of Vaginal canal with a distinctive flexure: The anterior ovary is shorter than the posterior one. V=35.94845.9 (n=36, r=43 55, SE = 0.50) . Cuticle thicker, the cuticle thickness at the vagina 11.9,at the posterior end 22.6 (n=34, r=13.1 41.8, SE=1.36) . Male:Body length 14.1mm(n = 32,r = 7.8 17.6,SE = 0.37).Width at the midbody 120 (n=32, r=89-144, SE=2.42) .Two separate curved spicules are not uniform in length,the longer spicule length 339 (n=32,r=280 410, SE=5.6), ratio of body length to spicule length is 41.7 (n=32, r=27.6 51.5, SE=0.95),the shorter spicule length 327 (n=32, r=251 400, SE=6.9) ,Caudal papillae in three rows, the middle row with 34, lateral rows 22. Diagnosis: (1) R..yunanensis is separated from the other species of the genus with the exception of R.jingdeensis, R.wuchangensis, R.culicivorax and R.iyengari by the distinct flexure of its vagina. (2) It differs from R.culicivorax (25.2) and R. iyengari (26.2) and R.siehuanensis (22.7) in its larger ratio of body length to sp icule length (41.7) . (3) The position of the vulva is more anterior in R.yunan- ensis than in R.jingdeensis (P<0.01). Besides that, the length of two ovaries are not uniform in R. yunanensis (V=35.94845.9), but almost uniform in R.jingdeensis (V=4031.841) and the ratio of body length to spicule length in R.yunanensis is also larger than in R.jingdeensis (37.8).(4)The ratio of its body length to spicule length differs from that of R.wuchangensis (35.7)and the position of vulva is more anterior than that of R.wuchangensis (>50%), the two ovar
