Key to the genera of Blastobasinae of Costa Rica based on males

1. First flagellomere dilated, forming a notchlike space between dilated part and flagellomeres 2–4 (Figs. 76–311).. Blastobasis

- First flagellomere not modified as above................................................................... 2

2. Labial palpus diminutive or extending slightly beyond midlength of frontoclypeus............................ Pigritia

- Labial palpus extending to or beyond vertex................................................................ 3

3. Juxta present......................................................................................... 4

- Juxta absent.................................................................................... Koleps

4. Juxta bandlike or platelike (ex. Fig. 55).................................................................... 5

- Juxta divided mesially (ex. Fig. 53)............................................................. Pseudokoleps

5. Proximal flange present................................................................................ 6

- Proximal flange absent................................................................................. 8

6. Apical process of ventral part of valva elongate, directed inwardly and overlapping............................ Pheos

- Apical process of ventral part of valva not directed inwardly and overlapping...................................... 7

7. Proximal flange protuberant from inner surface of dorsal part of valva.................................... Hypatopa

- Proximal flange not protuberant from inner surface of dorsal part of valva................................... Pigritia

8. Basal region of dorsal part of valva developed laterally into a large upturned lobe bearing 1−2 large, spinelike, apical setae (Figs. 57, 59).................................................................................. Hallicis

- Middle region of dorsal part of valva developed into a large, ventrally projecting lobe (Figs. 61, 63)............ Barbaloba