Key to species of Carinostigmus from the Indian subcontinent (based on females)

1. Mandibles bidentate................................................................................... 2

- Mandibles tridentate................................................................................... 3

2. Inner and outer mandibular tooth almost equal in length; metanotum with parallel vertical ridges converging slightly toward middle; following structures white: palpi, basal half of mandible, apex of labrum, underside of scape, and pronotal tubercle.................................................................................. C. bucheilus Krombein

- Inner mandibular tooth distinctly shorter than outer; metanotum smooth without parallel vertical ridges; only pronotal lobe yellowish white to white, other structures testaceous............... C. parliensis Tessy, Sureshan & Girish Kumar, sp. nov.

3. Face with median ridge weak, without projection near middle [Figure 19 of Krombein (1984)]; groove along inner eye margin weakly crenulate; metasomal petiole stouter [Figure 48 of Krombein (1984)], 4× as long as median width................................................................................................. C. clypeolus Krombein

- Face with median carina stronger and armed with erect projection near middle [Figure 18 of Krombein 1984]; groove along inner eye margin strongly crenulate; metasomal petiole more slender [Figs 49–52 of Krombein (1984)], 5–8.5 × as long as median width............................................................................................... 4

4. Petiole stouter [Figure 51 of Krombein (1984)], about 5–6.5 × as long as median width.............................. 5

- Petiole more slender [Figures 49, 50 of Krombein (1984)], 7.5–8.5 × as long as median width........................ 7

5. Propodeal enclosure except basal section with irregular oblique transverse striations and smooth area posteriorly (Fig. 18); apex of clypeus almost rounded, not emarginated.................. C. nepalensis Tessy, Sureshan & Girish Kumar, sp. nov.

- Propodeal enclosure except basal section rugoso-reticulate (Figs 28 & 37); apex of clypeus slightly emarginated.......... 6

6. Underside of head with strong longitudinal costae except median area with delicate longitudinal lineolations narrowly (Fig. 24); mandible with narrow ivory streak near base............................................... C. costatus Krombein

- Underside of head moderately densely punctate especially towards middle and usually with few parallel carinae laterally (Fig. 33); mandible with no ivory markings.................................................... C. aterrimus (Turner)

7. Declivous surface of pronotum anterior to transverse ridge smooth or with only evanescent irregular rugulae; interocular distance at anterior ocellus 1.4–1.5 × that at antennal insertions.................................. C. congruus (Walker)

- Declivous surface of pronotum anterior to transverse ridge with vertical rugae; interocular distance at anterior ocellus 1.2–1.3 × that at antennal insertions............................................................ C. griphus Krombein