A SIMPLIFIED KEY TO EUROPEAN COLOBOSTEMA (males only, exclusive of the Mediterranean region)

A complete key to the West Palaearctic species of the genus will be provided in the second part of this revision. The simplified key below, essentially based upon characters of the male genitalia and of the pregenital segment, allows the identification of the temperate and boreal European representatives of the genus that are dealt with in the first part. Great care should be exercised regarding the shape of tergite 7, the appearance of which varies considerably according to the angle of view. Furthermore, it may be markedly distorted in dried specimens. To ensure a safe identification, it is highly advisable to cut and clear the tip of abdomen in potash.

1. Tergite 7 very short, about 3 times as wide as long (Fig. 10 A); gonocoxites broadly truncate apically (Fig. IOC) .............................. C. schertenleibi sp. n.

— Tergite 7 longer, as long as wide, or at most twice as wide as long; gonocoxites never broadly truncate apically...........................................................................2

2. Posterior margin of tergite 7 deeply emarginate (Fig. 9 A); gonocoxites large, gradually narrowing towards apex (Fig. 9 C).... C. obscuritarse (Strobl)

— Tergite 7 variously produced posteriorly or at most only slightly emarginate on posterior margin.............................................................................................3

3. Apical lobes of epandrium rounded (Fig. 4 D); posterior margin of tergite 7 sinuous or shallowly emarginate (Fig. 4 A) ............................... C. geigeri sp. n.

— Apical lobes of epandrium acute; posterior margin of tergite 7 differently shaped ................................................................................................................. 4

4. Posterior margin of tergite 7 with 4 lobes, the submedian pair slightly asymmetrical, not much more developed than lateral pair (Fig. 2 A); gonocoxites bearing an acute inner basal process (Fig. 2 C).... C. dudai Krivosheina

— At most 3 projections on posterior margin of tergite 7, median one usually much more developed than lateral ones, or tergite 7 nearly square or roughly pentagonal in shape.............................................................................................5

5. Gonocoxites massive, apically not narrowed (Fig. 3 C); tergite 7 with a broadly triangular median projection on posterior margin (Fig. 3 A) ......................... ................................................................................... C. flavimanum (Strobl)

— Gonocoxites more slender, broadly triangular, always narrowing towards apex .................................................................................................................. 6

6. Tergite 7 roughly square or pentagonal, or posterior margin produced into a broad, practically straight median projection (Figs 1 A-B, 11 A) ...................... 7

— Posterior margin of tergite 7 produced into a narrow elongate median projection, which is rounded or narrowly truncate apically, surrounded by a pair of much shorter, more or less developed lateral projections (Figs 5 A, 6A, 7A, 8A)..................................................................................................................8

7. Tergite 7 pentagonal or square, with a short rounded median posterior projection (shape varying according to angle of view) (Figs 1 A-B); epandrium with slightly asymmetrical apical lobes, which are comparatively longer and acute (Fig. IE) .......................................................................... C. auberti sp. n.

— Posterior margin of tergite 7 with a broad, truncate median projection (Fig. 11 A); epandrium with symmetrical short and blunt apical lobes (Fig. 11 D) ...................................................................................... C. triste (Zetterstedt)

8. Epandrium strongly asymmetrical apically, with one lobe much more developed than the other (Fig. 6 D); sternite 7 deeply emarginate posteriorly, with strongly developed lateral projections (Fig. 6 B) ..................... C. infumatum (Haliday)

— Epandrium with apical lobes symmetrical or only weakly asymmetrical; sternite 7 only weakly emarginate posteriorly ........................................................ 9

9. Epandrium with very acute, horn-like apical projections, which are directed posteriorly more or less obliquely (Fig. 5 D) .................. C. griseinerve (Duda)

— Epandrium with apical lobes acute, directed laterally (Figs 7 D, 8D).... 10

10. Median projection of posterior margin of tergite 7 rounded apically (Fig. 8 A); gonocoxites strongly narrowed in distal half, with apex appearing blunt in ventral view (Fig. 8 C); aedeagus short (Fig. 8 C).... C. nigripenne (Meigen)

— Median projection of posterior margin of tergite 7 clearly truncate apically (Fig. 7 A); gonocoxites less strikingly narrowed in distal part, with apex acute (Fig. 7 C); aedeagus elongate (Fig. 7 C) ................................. C. lastovkai sp. n.