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I see only this alternative:
3. Surstylus in lateral view curved in an arc; epandrial lobe slender and not bilobed (Fig. 13). Prescutellar patch usually well defined in both sexes....... tenellus (Wiedemann)
- Surstylus in lateral view almost straight; epandrial lobe bilobed with ventral lobe itself trilobed apically (Fig. 11). Prescutellar patch often reduced or absent in female ........................... silaceus Chandler et Negrobov (2008: Dipterists Digest 15: 34, British species)