Genus Baiyuerius Zhao, B. Li & S. Li, 2023

Type species. Baiyuerius zuojiang Zhao, B. Li & S. Li, 2023

Diagnosis. Baiyuerius resembles Yunguirius B. Li, Zhao & S. Q. Li, 2023 in 1) carapace with high and broad cephalic region, and legs usually red or orange (Figs 6A, B, 10A, B, 24A, B; fig. 4A, B in Liu et al. 2020; fig. 4A, B in Luo et al. 2023; fig. 7A, B in Wei et al. 2024); 2) conductor large and crescent, with modified dorsal margin, median apophysis human-ear-shaped (Fig. 1A–E; fig. 317 in Wang et al. 2012); 3) epigyne with large atrium, and copulatory ducts with distinct blind sac (Fig. 2A–D; figs 2A, B, 8A, B in Wei et al. 2024). But males of Baiyuerius are diagnosed by the process on the dorsal margin of the conductor strongly sclerotized, except of the digitus- group species, which without the process (Fig. 1A–E) [vs. weakly sclerotized in the Yunguirius (fig. 317 in Wang et al. 2012)]; 2) embolic base enlarged (Fig. 1A–E) [vs. not so large in Yunguirius (fig. 317 in Wang et al. 2012)]. Females are distinguished from those of Yunguirius by 1) atrium without anterior margin, and the epigynal plate without sclerotized structure above atrium (Fig. 2A, C) [vs. atrium with or without anterior margin, but the epigynal plate with sclerotized part above atrium (fig. 3A in Zhao et al. 2023; figs 2A, 8A in Wei et al. 2024)]; 2) spermathecae nearly spherical, sometimes with tubercles (Fig. 2B, D) [vs. long and divided into two parts (fig. 2B in Zhao et al. 2023; fig. 2B in Wei et al. 2024)].

Key to the Baiyuerius species groups

1. Male............................................................................................... 2 Female (those of cuii and digitus -species groups unknown).................................................... 6

2. Dorsal margin of conductor without modified process (Fig. 21B)............................... digitus- species group Dorsal margin of conductor with modified process.......................................................... 3

3. Patella with two apophyses (Figs 17C, 19C).................................................. cuii -species group Patella with only one apophysis......................................................................... 4

4. Patellar apophysis thick and cylindrical, lateral tibial apophysis expanded and round, conductor dorsal apophysis extremely long (Figs 27C, D, 31C, E)........................................................... zuojiang -species group Patellar apophysis with pointed tip, lateral tibial apophysis long, with pointed tip, conductor dorsal apophysis short....... 5

5. Process of dorsal margin of conductor strongly sclerotized and divided into two branches, tegular sclerite Y-shaped (Fig. 1C in Hoang et al. 2023)................................................................... rotulus -species group The process with a distinct basal stalk and separated from dorsal margin of conductor, tegular sclerite not Y-shaped (Figs 3B, 5B, 11B).......................................................................... chongzu -species group

6. Epigynal teeth present (Figs 9A, 13A, 15A).............................................. chongzu -species group Epigynal teeth absent.................................................................................. 7

7. Epigynal plate large, width of epigynal pocket subequal to length, copulatory ducts long, without blind sacs (Figs 23A, B, 25A, B)................................................................................ rotulus -species group Epigynal plate relatively small, width of epigynal pocket obviously longer than length, copulatory ducts short, with blind sacs (Figs 29A, B, 33A, B)............................................................... zuojiang- species group