Rheumatogonus vietnamensis Zettel & Chen Fig. 38 Rheumatogonus vietnamensis Zettel & Chen 1996: Entomol. Abhand. Mus. Tierk. Dresden 171–175. Diagnosis. Males of R. vietnamensis can be distinguished by the parameres with a longer parallel-sided shaft with a negligible basal tooth (Fig. 38), whereas R. intermedius has semicircular parameres with a pronounced basal tooth (Fig. 39). Females of R. vietnamensis can be distinguished by the mesothorax with a distinct and longer dark hair patch and longer body length of 5.65–6.40 mm, whereas R. intermedius has a less distinct and shorter dark hair patch and shorter body length of 5.55–5.60 mm (Zettel & Chen 1996). Discussion. This species previously was reported from Indonesia, Thailand, and Vietnam (Zettel & Chen 1996). In this study, this species was collected from Kanchanaburi and Ratchaburi provinces. This species exhibits variation in coloration, size, and genitalic structure. The populations of R. vietnamensis from Kanchanaburi and Ratchaburi provinces are morphologically very similar to those of R. intermedius from Ratchaburi and Prachuap Khiri Khan provinces. Moreover, using size to distinguish females of these two species is not reliable because we have found overlap in body length values. Previously, the distributions assisted in the identification of these two species; however, these new data reveal that the ranges of these two species overlap in this region. Thus, the structure of parameres is the only reliable character that can be used to distinguish these two species. High levels of intraspecific variation have been reported in several other members of this subfamily (e.g., Ptilomera tigrina, Pleciogonus wongsirii). This species did not occur synoptically with its congener in this study. Material examined. THAILAND: Kanchanaburi Province: Amphur Thong Pha Phum, Heuy Ou Long, stream, 14º46'N 98º40'E, 139 m, 11-IV-2002, UMC and CMU teams, L-332 (1 male, 4 females); Amphur Sai Yok, Thong Pha Phum Reforestation, Mae Nam Noi, 14º31'N 98º37'E, 204 m, 12-IV-2002, UMC and CMU teams, L-335 (3 males, 3 females); Amphur Sang Khla Buri, Heuy Kob, 15º13'N 98º22'E, 289 m, 13-IV-2002, UMC and CMU teams, L-339 (3 males, 4 females); Thong Pha Phum Reforestation Station, creek behind main office, 14º39'N 98º35'E, 211 m, 14-IV-2002, Vitheepradit and Kirawanich, L-341 (9 males, 10 females); Amphur Thong Pha Phum, Heuy Ka Yaeng at Ban Padsadoo Klang, 14º33'N 98º34'E, 296 m, 9-IV-2003, Sites, Vitheepradit, Prommi and Setaphan, L-457 (2 males, 2 females); Amphur Thong Pha Phum, Heuy Ka Yaeng at Ban Pra Jam Mai, 14º35'N 98º34'E, 247 m, 9-IV-2003, Sites, Vitheepradit, Prommi and Setaphan, L-458 (1 male, 2 females); Amphur Sai Yok, Thong Pha Phum Reforestation station, Mae Nam Noi, 14º31'N 98º37'E, 204 m, 10-IV-2003, UMC and CMU teams, L-462 (1 female); Amphur Thong Pha Phum, Heuy Ou Long, 14º46'N 98º40'E, 139 m, 12-V-2003, Vitheepradit, Prommi and Ferro, L-525 (8 males, 11 females); Amphur Sangkhla Buri, Heuy Li Jia, 15º04'N 98º33'E, 169 m, 12-V-2003, Vitheepradit, Prommi and Ferro, L-526 (11 males, 6 females); same locality, 26-XI- 2010, KU team, C-9 (1 female); Amphur Sangkhla Buri, Heuy Li Jia, 15º04'N 98º33'E, 169 m, 26-V-2004, Vitheepradit and Prommi, L-718 (1 male 4 females); Thong Pha Phum NP, Huey Pak Khok, 14º38.738'N 98º31.374'E, 187 m, 25-XI-2006, KU team, C-6 (2 females); Sai Yok NP, Mae Nam Noi, 14º26.820'N 98º48.085'E, 79 m, 24-XI-2010, KU team, C-4 (1 female); Heuy Clity, 14º57.717'N 98º54.552'E, 674 m, 26-XI-2010, C-10 (6 males, 1 female); same locality, KU team, C-256 (1 male, 2 females); Lum Klong Ngu NP, Nangkruan Waterfall, 14º54.306'N 98º43.539'E, 605 m, 22-I-2013, KU team, C-257 (1 male, 3 females); Ratchaburi Province: Amphur Suan Phuen, 14.6 km SSE Suan Phueng, 13º28'N 99º15'E, 183 m, 17-IV-2002, Vitheepradit and Kirawanich, L-352 (1 male); Heuy Kog Moo, 13º27.786'N 99º15.210'E, 198 m, 13-XII-2012, KU team, C-88 (10 males, 7 females); Amphur Suan Phueng, Pachi River WS, KU team, C-195 (10 males, 6 females).

Published as part of Raruanysong, Sajeemat, Vitheepradit, Akekawat & Sites, Robert W., 2014, Key to the species of Ptilomerinae (Hemiptera: Heteroptera: Gerridae) of Thailand and review of the fauna of the Tennaserim Mountain Range, pp. 101-117 in Zootaxa 3852 (1) on page 112, DOI: 10.11646/zootaxa.3852.1.4, http://zenodo.org/record/230500