A revision of Rhombuniopsis Haas, 1920 (Unionida, Unionidae) endemic to the ancient lakes of Yunnan, China, with descriptions of two new species Author Xiang, Hong Quan Yuxi Agriculture Vocation-Technical College Department of Animal Science. Yuxi 653106, China Author He, Yue Ming College of Engineering and Technology, Tianjin Agricultural University, Tianjin 300384, China Author Zhang, Le Jia Museum für Naturkunde, Leibniz, Institut für Evolutions und Biodiversitätsforschung, Berlin 10115, Germany Author Gao, Han Fuzhou University College of Computer and Data Science / College of Software, Fuzhou 350108, China Author Guo, Liang Fuzhou Wilds of Insects Cultural Creativity Co., Ltd., Fuzhou 350025, China Author Lu, Yi Zhi Auburn University, Auburn, AL 36849, Alabama, United States of America Author Fan, Shu Yun Kunming Institute of Fishery Sciences, Kunming 650021, China Author Chen, Hui Jiangsu Key Laboratory for Biodiversity and Biotechnology, College of Life Sciences, Nanjing Normal University, Nanjing 210023, China text Zootaxa 2024 2024-07-16 5481 2 273 289 http://dx.doi.org/10.11646/zootaxa.5481.2.6 journal article 10.11646/zootaxa.5481.2.6 1175-5326 12749748 80194D39-74AD-4C40-AAAC-C2F52D4FF179 Rhombuniopsis songmeng Xiang, He & Zhang sp. nov. Fig. 9A–F Etymology: Derived from ‘Songmeng ( ẇDz )’, the old name of present Songming County, where its type locality (Lake Babuhai) is located. The recommended Chinese name of this species is “ ẇDzmṉü ” (Pseudomonas aeruginosa). Material examined. Holotype : Length 46.3 mm , from Lake Babuhai , Yanglin town ( êūDz ), Songming County , Kunming , Yunnan Province , China , 25.277047°N , 103.093158°E , 2021.6., collected by Hong Quan Xiang ( KIZ1904601 ) (Fig. 10 A). Paratypes : 10 specimens ( KIZ1904602 – KIZ1904611 ): KIZ1904602–KIZ1904611, Lake Babuhai , Yanglin town , 25.277047°N , 103.093158°E , 2021.6., collected by Hong Quan Xiang. Other-localities : Lake Lulianghai , Zhongshu Town ( 中NJDz ), Luliang County , 25.01131°N , 103.66032°E , 2023.9.1 . ( KIZ1904612 – KIZ1904614 ), collected by Hong Quan Xiang. Diagnosis. Shell ovate, periostracum dark brown to black, pseudocardinal tooth of the right valve with a thin groove at the top. FIGURE 9. Shell of Rhombuniopsis songmeng sp. nov. A. Holotype collected from Lake Babuhai, KIZ1904601, shell length 46.3 mm. B–D. Specimens collected from Lake Babuhai, KIZ1904602–KIZ1904604, shell length 45.3 mm, 40.0 mm, and 33.2 mm. E–F. Specimens collected from Lake Lulianghai, KIZ1904612–KIZ1904613, shell length 58.0 mm and 62.0 mm. Scale bars: 1 cm. Description. Shell(Fig. 10A–F). Length 18–60 mm . Shell small, solid, of medium thickness, ovate, symmetrical; posterior margin ovate, ventral margin straight; the umbo with wavy wrinkles, often eroded; lateral teeth long; the left valve with two pseudocardinal teeth, divided to two opposite triangles by a slit, pseudocardinal tooth of the left valve with a thin groove at the top, connected to lateral teeth; ligament long; anterior adductor muscle scar deep, posterior adductor muscle scar relatively small. Periostracum shining black; nacre white, with non-obvious fine lines. Comparison. This species can be differentiated from the most similar species R. tauriformis by having a relatively narrow shell, weak lines on the nacre, and a more backward umbo position. Habitat and distribution: Extinct species that inhabited muddy to sandy substrates near tributary mouths of Lake Babuhai.