1. Setae se 1.3–2 times longer than si.............................................................................................................................. 9

– Setae si and se subequal in length................................................................................................................................ 2

2. Setae cG I microspines, of same shape as cG II; distance se–se 3–6 times greater than si–si...................................... 6

– Setae cG I filiform (in some specimens of Y. faini setae cG I microspines), different in shape from microspines cG II; distance se–se about 7 times greater than si–si........................................................................................................... 3

3. Distance se–se about 4–5 times greater than si–si. Posterior projections of coxal fields I 1.5–1.7 wider than long... 4

– Distance se–se about 7 times greater than si–si. Posterior projections of coxal fields I 2.8 times wider than long...... Y. faini Hyland et Clark, 1959 (Figs. 68, 69A–K)

4. Setae cp 1.3–2 times longer than c3............................................................................................................................. 5

– Setae cp and c3 subequal in length..................................... Y. microti Smith, Whitaker et Giesen, 1985 (Fig. 64A–I)

5. Setae cp 2 times longer than c3. Distances 4a–4a and ps3–ps3 subequal, 18–20 long........................................................................................................................................................... Y. alticola Zabludovskaya sp. nov. (Fig. 67A–H)

– Setae cp 1.3–1.8 times longer than c3. Distance 4a–4a 23–26, 1.6–1.8 times greater than ps3–ps3, 13–16.................................................................................................................................. Y. ascanicus Zabludovskaya, 1989 (Fig. 66)

6. Alveoli of setae h1 and h3 absent. Posterior projections of coxal fields I 1.4–4 times wider than long..................... 7

– Alveoli of setae h1 and h3 present. Length and width of posterior projections of coxal fields I subequal............................................................................................................. Y. hylomyscus Bochkov et OConnor sp. nov. (Fig. 63A–H)

7. Distance se–se 5–8 times greater than si–si. Posterior projections of coxal fields I 1.4–2.1 wider than long............ 8

– Distance se–se about 3 times greater than si–si. Posterior projections of coxal fields I 4 times wider than long......... .................................................................................................. Y. lophuromys Bochkov et OConnor sp. nov. (Fig. 57)

8. Body length, including gnathosoma, 370–380 long. Propodonotum covered by rectangular-like ornamentation. Hysteronotal scale-like pattern of idiosoma weakly developed. Setae si and se 18–20 and 19–22 long, respectively; setae c3 and cp subequal in length................................................... Y. otomys Bochkov et OConnor sp. nov. (Fig. 62A–F)

– Body length, including gnathosoma, 305–330. Propodonotum covered by striations. Hysteronotal scale like pattern of idiosoma distinctly developed. Setae si and se 26–35 and 26–30 long, respectively. Setae cp about 2 times longer than c3........................................................ Y. apodemi Fain, Lukoschus, Jadin et Ah, 1967 stat. nov. (Fig. 56A–H)

9. Posterior projections of coxal fields I 1.2–2.1 times longer than wide. Setae pR I–II present................................... 10

– Posterior projections of coxal fields I 0.7 times longer than wide. Setae pR I–II absent............................................................................................................................................ Y. limnomys Bochkov et OConnor sp. nov. (Fig. 55A–H)

10. Setae si and se 30–35 and 50–55 long, respectively. Bursa copulatrix opening dorsal. Propodosoma bearing 2 pairs of distinctly developed and slightly sclerotized folds ventrally................................................................................. 11

– Setae si and se 13–15 and 27–30 long, respectively. Bursa copulatrix opening terminal. Propodosoma bearing 2 or more pairs of weakly developed folds ventrally.............................................................. Y. muris Fain, 1957 (Fig. 52)

11. Body, including gnathosoma, 350–365 long. Setae 1a 13–16 long; setae c3 18–22 long; setae cp 2.3–2.7 times longer than c3. Posterior projections of coxal fields I about 2.1 times wider than long........................................................................................................................................................................... Y. rattus Bochkov et OConnor sp. nov.

– Body, including gnathosoma, 370–390 long. Setae 1a 9–13 long; setae c3 11–16 long; setae cp 1.9–2.3 times longer than c3. Posterior projections of coxal fields I about 1.4 times wider than long........................................................................................................................................................... Y. apomys Bochkov et OConnor sp. nov. (Fig. 54A–H)