Key to species of the genus Betasyringophiloidus

(females)

* species occurring in the Nearctic region.

1. Each branch of peritremes with less than 12 chambers. Dorsal setae thick......................................... 2

- Each branch of peritremes with 13–14 chambers. Dorsal setae thin............................................. 4

2. Length ratio of setae vi: si 1:4–5.5. Setae ag3 1.2–1.3 times longer than ag1 ....................................... 3

- Length ratio of setae vi: si 1:3. Setae ag3 1.7–1.8 times longer than ag1 ........ B. motacillae (Bochkov and Mironov, 1998)

3. Hysteronotal shield fused with pygidial shield......................................... B. saxicolus Skoracki, 2011

- Hysteronotal shield not fused with pygidial shield................................ B. seiuri (Clark, 1964) comb. nov. *

4. Setae ag1 and ag2 subequal in length. Setae c1, c2 and d1 shorter than 170. Stylophore 150 long................................................................................................... B. phoenicurus Skoracki, 2011

- Setae ag1 1.6–1.8 times longer than ag2. Setae c1, c2 and d1 longer than 190. Stylophore 170–180 long............................................................................................. B. schoeniclus (Skoracki, 2002)