Key to genera of Gymnodamaeidae in North America

1 Genital and anal plates share a common opening, and are separated by soft cuticle, rather than a sclerotized ano-genital bridge; preanal organ hinged to spurs from ventral plate (Figs. 4, 7) .................................................................... 5

- Genital and anal plates separated by a distinct band of sclerotized cuticle (the ano-genital bridge) under which the preanal organ is inserted (Figs. 12, 23) ........................................................................................................................ 2

2 Distal segments of the legs with cup-like basal retrotectum forming a ball-and-socket joint with previous segment (Figs. 13–14 arrows); lamellar seta (le) inserted laterally near rostral seta (Fig. 10); notogaster gently convex dorsally ................................................................................................................................ Adrodamaeus Paschoal, 1982

- Distal segments of the legs without cup-like basal retrotectum (Fig. 8); lamellar seta inserted dorso-medially, distant from rostral seta (Figs. 6, 31, 36); notogaster flattened to concave (Figs. 17, 22) ....................................................... 3

3 Interlamellar setae inserted between bothridia, on relatively small apophyses, bothridial ridge absent; 4 pairs notogastral setae (h 1, p 1-3), seta h 2 absent (Fig. 24); medial margin of genital shields smooth, without interlocking teeth; small mites with ventral lengths <0.4 mm .................................................................................................................. 4

- Interlamellar setae inserted anterior to bothridia, on strong apophyses at median corner of bothridial ridges (Fig. 18 arrow); 5 pairs notogastral setae (h 1-2, p 1-3); medial margin of genital shields each with a series of teeth that interlock in a zipper-like fashion (Fig. 19); large mites with ventral length 0.73–0.9 mm ........ Odontodamaeus Paschoal, 1982

4 Apophyses of posterior notogastral setae h 1, p 1 strongly developed and clustered medially (Figs. 20-21); 7 pairs of genital setae, g2 posterior and lateral to g1; notogastral cerotegument with raised cell in mature adults...................... ................................................................................................................................................... Jacotella Banks, 1947

- Apophyses of posterior notogastral setae variously developed, but not clustered medially (Fig. 24); 6 pairs of genital setae, g2 inserted posterior to g1 and in line with other genital setae; notogastral cerotegument forming series of longitudinal folds in cerotegument (Fig. 22) ............................................................................ Joshuella Wallwork, 1972

5 Notogaster with a maximum of 5 pairs of setae, seta h3 absent; bothridial rim without posterior tooth .................... 6

- Notogaster with 6 pairs of setae including h3 inserted about midway between lyrifissures im and ip; bothridial rim with posterior tooth (Fig. 15) ................................................ Donjohnstonella nom. nov. (pro Johnstonella Paschoal)

6 Notogastral cerotegumental pustules spherical (Figs. 3, 28); prodorsum with interlamellar setae opposed to distinct median tubercle and forming enantiophysis (Figs. 1–2, 31)......................................................................................... 7

- Notogastral cerotegumental pustules longer than their diameter, bullet-shaped to digitiform, resembling morel mushrooms (Figs. 35, 39); interlamellar setae not opposed to median tubercle (which is poorly developed or absent) ......................................................................................................Roynortonella nom. nov. (pro Nortonella Paschoal)

7 Cerotegument on notogaster without raised pattern of ridges or cells (Fig. 27), but with anterior median patch of strong tubercles (Figs. 29–30); posterior seta h 1 inserted on posterior wall of notogaster; pedotectum II acuminate distally (Fig. 31) ............................................................................................................... Pleodamaeus Paschoal 1982

- Cerotegument on notogaster with lateral folds and with median pattern of raised ridges (sometimes forming closed cells) in mature adults (Fig. 5); posterior notogastral seta h 1 on dorsal surface of notogaster; pedotectum II with rounded margin (Fig. 2) ........................................................................................... Gymnodamaeus Kulczynski 1902