Key to the adult males of Sericostoma in Turkey

1. In lateral view, mesoventral branch of each lateral prolongation of segment X directed ventrad......................….2

- Mesoventral branch directed posterad or posteroventrad....................................................... 3

2. Mesoventral branch of each lateral prolongation of segment X short, stout, truncate at apex (Figs 7, 8............... S . ida

- Mesoventral branch long, triangular, pointed at apex (Figs 12, 13)..................................... S. grusiense

3. Mesoventral branch of each lateral prolongation shorter than half as long as dorsal branch….......... .. S. mesopotamicum

- Mesoventral branch at least half as long as dorsal branch.......................................................4

4. Mesoventral branch of each lateral prolongation of segment X half as long as dorsal branch.......................... 5

- Mesoventral branch of each lateral prolongation more than half as long as dorsal branch............................. 7

5. Mesoventral branch of each lateral prolongation of segment X nearly parallel-side and close to dorsal branch in lateral view. ................................................................................................... 6

- Mesoventral branch triangular and widely separated from dorsal branch in lateral view..................... S. flavicorne

6. Preanal appendages digitate, smaller than obliquely truncate basoventral branches of lateral prolongations of segment X in lateral view; in dorsal view, dorsal branches of lateral prolongations each bearing small, pointed subapical projection on inner edge..................................................................................... S. taskent sp. n.

- Preanal appendages clavate, larger than acute basoventral branches of lateral prolongations; in dorsal view, dorsal branches of lateral prolongations without small, pointed subapical projections................................ S. yuvarlakcay sp. n.

7. Dorsal branches of lateral prolongations of segment X slender in dorsal and lateral views; mesoventral branches 2/3 as long as dorsal branches (Fig. 36); apical dilatations of ventral branches of inferior appendages small (Fig. 38).... S. pinargozu sp. n.

- Dorsal branches of lateral prolongations thick in dorsal and lateral views; mesoventral branches of lateral prolongations more than 2/3 as long as dorsal branches; apical dilations of ventral branches of inferior appendages enlarged................. 8

8. Mesoventral branch of each lateral prolongation of segment X 4/5 as long as dorsal branch (Fig. 26); ventral branches of inferior appendages sinuate, apicomesally quadrangular in ventral view (Fig. 28)...................... S. dimcay sp. n.

- Mesoventral branch of each lateral prolongation 3/4 as long as dorsal branch; ventral branches of inferior appendages straight, apicomesally triangular in ventral view (Fig. 24)................................................... S. alakir sp. n.