Rhombuniopsis tauriformis Fulton, 1906

Fig. 4 A–F

Unio (Cuneopsis) tauriformis Fulton (1906): 246, pl. 9, fig. 9 [‘ Yunnan fu’ = Kunming, Yunnan Province, China].

Cuneopsis tauriformis Simpson (1914): 948 –949.

Rhombuniopsis tauriformis Haas (1920): 146 –151; Haas (1924): 185; Thiele (1934): 779–1022; Haas (1969): 269–270; Du et al. (2011): 216; He & Zhuang (2013): 100, Figs 235–236; Zieritz, Bogan, Froufe et al. (2018): 29 –44; Graf & Cummings (2021): 15; Liu, Liu, Wu et al. (2022): 1–37.

Rhombuniopsis cuneopiformis Huang & Zhang (1990): 69 –75; Du et al. (2011): 216.

Material examined. Newly collected material. Adult shell: Lake Dianchi, Shangsuan Town (上ũDz), 24.695185°N, 102.689200°E, 2017.11. (KIZ1904101 – KIZ1904103), collected by Jiao Wei Ning and Hong Quan Xiang ; Lake Dianchi, Xiaoqinghe Village (小DZāñ), 24.695185°N, 102.689200°E, 2019.6. (KIZ1904104 – KIZ1904105), collected by Liang Guo ; Lake Dianchi, Haikou (DZ口), 24.78012°N, 102.62258°E, 2023.5. (KIZ1904106 – KIZ1904110), collected by Hong Quan Xiang ; Lake Lulianghai, Zhongshu Town (中NJDz), Luliang County, 25.01131°N, 103.66032°E, 2023.9.1. (KIZ1904111 – KIZ1904113), collected by Hong Quan Xiang .

Diagnosis. Shell ovate to triangulate ovate, dark brown to black; umbo near to the front, with wavy wrinkles.

Description. Shell (Fig. 4 A–F). Length 20–55 mm. Shell small, thick, obliquely ovate, symmetrical or slightly asymmetrical, wedge-shaped, anterior margin truncate, posterior margin sharp or round; periostracum shining black, the umbo sculptured with wavy wrinkles, often eroded. Anterior adductor muscle scar oval, very deep; posterior adductor muscle scar round to oval, shallow. Left valve with two pseudocardinal teeth, anterior tooth rather thin, posterior tooth thick; anterior pseudocardinal tooth of the right valve well developed, spherical; lateral teeth long and thick; nacre white.

Comparison. This species can be differentiated from the most similar species R. songmeng sp. nov. by having a relatively prominent umbo and an obliquely ovoid shell.

Taxonomic remarks. Fulton (1906) described Unio (Cuneopsis) tauriformis based on shells collected from Kunming. According to the morphology of its shell, Haas (1920) assigned this species to Rhombuniopsis . Huang & Zhang (1990) described a new species, Rhombuniopsis cuneopiformis from shells collected at Lake Dianchi, but our morphological comparison confirms that it should be a synonym of R. tauriformis .

Habitat and distribution. Lives on muddy to sandy substrates, mostly found along the shores of lakes and where rivers enter the lakes at depths of 0–3 m. Known to occur in the Dianchi and Lulianghai lakes.