Rhombuniopsis linan Xiang, He & Zhang sp. nov.

Fig. 8A–I

Etymology: Derived from ‘Linan (临AE)’, the ancient name of Jianshui County in Honghe Hani and Yi Autonomous Prefecture, Yunnan Province. The recommended Chinese name of this species is “ 临AEmṉü ” (Lin'an pearl clam).

Material examined. Holotype: Length 61.4 mm, from Lake Yilong, Shigang Village (ƋṄñ), 102.615266°E, 23.666839°N, 2023.4., from Hong Quan Xiang and Yue Ming He. (KIZ1904501)(Fig.8 A) .

Paratypes: 10 specimens (KIZ1904502–KIZ19045011): KIZ1904502, Lake Yilong, Lulai Village (Rẍñ), 102.596596°E, 23.655097°N, 2023.3., from Jiao Wei Ning ; KIZ1904503, Lake Yilong, Shaba Village (Ủ坝ñ), Baxin Town, Shiping County, Yunnan Province, China, 102.628906°E, 23.658542°N, 2023.1., coll. Hong Quan Xiang. KIZ1904504 – KIZ1904511, Lake Yilong, Shigang Village (ƋṄñ), 102.615266°E, 23.666839°N, 2023.4., from Hong Quan Xiang and Yue Ming He .

Other-location: Lake Fuxian, Yousuo Town (右ãñ), 102.908495°E, 24.631587°N, 2023.1.20.(KIZ1904512), from Chong Ye Li ; Lake Fuxian, 102.863819°E, 24.138159°N, 2023.7. (KIZ1904513), from Chong Ye Li ; Lake Qilu, Xiushan Street (WƜĕ), Tonghai County, 102.748644°E, 24.138159°N, 2022. (KIZ1904514), from Le Jia Zhang ; Lake Xingyun, Longjie Village (kĕñ), 102.806266°E, 24.385006°N, 2022.4. (KIZ1904515 – KIZ1904516), from Suo Zhu Yang ; Lake Xingyun, Longjie Village, 102.806255°E, 24.385000°N, 2022.4. (KIZ1904517), from Hong Quan Xiang .

Diagnosis. Shell round to ovate, periostracum dark brown to black; pseudocardinal tooth of the right valve in some individuals extend upward, the umbo with wavy wrinkles and wrinkles occur only on the umbo.

Description. Shell (Fig. 8 A–I). Length 20–78 mm. Shell large, round to ovate, thick, obese and inflated. Dorsal margin arched smoothly, anterior margin rounded, ventral margin slightly rounded; umbo located at 1/3 of the dorsal margin, sculptured with obvious and deep wavy wrinkles, the umbo has vertical stripes near the wrinkles, often eroded; ligament long. Lateral teeth long, the right valve with one extremely thick and raised pseudocardinal tooth, extending upward and having a groove in the upper part; the left valve with two pseudocardinal teeth, anterior tooth rather thin, posterior tooth thick. Anterior adductor muscle scar very deep, posterior adductor muscle scar relatively small; periostracum shining black or with brownish-yellow, nacre orange-yellow or white.

Comparison. This species can be differentiated from the most similar species R. fultoni by having a thick pseudocardinal tooth of the right valve, extending upward and having a groove in the upper part. The nacre of R. linan sp. nov. is sometimes orange-yellow, a color that has not been observed in other Rhombuniopsis species.

Habitat and distribution. Extinct species that inhabited muddy to sandy substrates near river mouths in Lake Yilong, Qilu, Xingyun, Fuxian.