Key to adults of species of Ceratoppia known from North America

1. Mentum of subcapitulum with two pairs of hypostomal setae................................................... 2

- Mentum of subcapitulum with one pair of hypostomal setae.................................................... 3

2. Two pairs of long posterior notogastral setae (p1, p3)..................................... C. bipilis (Hermann) group (Holarctic, widespread in North America)

- Two pairs of very short posterior notogastral setae (p1, p3)........................................ C. valerieae n. sp. (known from BC, AB, WA, OR, CA)

3. Two or three pairs of conspicuous notogastral setae........................................................... 4

- Notogastral setae reduced, much shorter than length of rostral setae.............................................. 8

4. Three pairs of notogastral setae long, conspicuous (h1, p2, p3).................................. C. sexpilosa Willmann (known from AK, YK, NT, NU)

- Two pairs of conspicuous notogastral setae................................................................. 5

5. Rostrum deeply indented with inset medial tooth; interlamellar setae distinctly shorter than length of lamellae; notogastral setae h1 and p3 expressed; barbed epimeral setae (3–1–2–3)....................................... C. indentata n. sp. (known from BC, WA, OR, CA)

- Rostrum not deeply indented, rounded (dentate) or with large medial tooth........................................ 6

6. Rostrum with strong medial tooth and lateral denticles; lamellae reaching insertion of rostral setae; interlamellae setae as long or longer than lamellae........................................................ C. quadridentata (Haller) group (Holarctic, widespread in northern North America)

- Rostrum rounded anteriorly, dentate, but without medial tooth; lamellae not reaching insertion of rostral setae............ 7

7. Large (700–1000 um); dark (almost black) in colour; lamellar setae longer than rostral setae; interlamellar setae as long as prodorsum, longer than lamellae; lamellae short cusps; two pairs of medium length posterior notogastral setae (p1, p3)............................................................................................ C. sphaerica (L. Koch) (known from AK, YK, NT, NU)

- Smaller species (550–650 um), reddish in colour, with prominent rostral bump in lateral view; two pairs of medium length posterior notogastral setae (p1, p3)............................................................ C. offarostrata n. sp. .......................................................................................(known from BC)

8. Three pairs of reduced notogastral setae (p1, p2, p3), in particular setae p2 minute, not discernable in all specimens; lamellae long, reaching insertion of rostral setae, with 2/3 free cusps; lamellar setae reduced, much shorter than rostral setae; large medial rostral tooth with lateral denticles; interlamellar setae long, reaching past tips of lamellae....... C. longicuspis n. sp. (known from BC, WA, OR, CA)

- Two pairs of reduced notogastral setae (p1, p3); lamellae with short cusps, not reaching insertion of rostral setae; interlamellar setae longer than lamellae; wide medial rostral tooth; smaller species (530–580 um).................. C. tofinoensis n. sp. (known from BC, WA, OR)