1a Cells are heterovalvate.............................................................................................................................................. F. heterovalvata
1b Cells are not heterovalvate.................................................................................................................................................................2
2a Valves with lateral area.......................................................................................................................................................................3
2a Valves without lateral area..................................................................................................................................................................9
3a Central area with stauros-like transverse expansion..........................................................................................................................4
3b Central area without transverse expansion.........................................................................................................................................5
4a Striae 16-18 in 10 μm............................................................................................................................................................. F. acuta
4b Striae 9-13, Areolae 35-40 in 10 μm............................................................................................................................. F. finmarchica
4c Striae 10-12, Areolae 26-29 in 10 μm.............................................................................................................................. F. krammeri
5a External terminal raphe fissure hooked..............................................................................................................................................6
5b External terminal raphe fissure simple or slightly bent......................................................................................................................8
6a Areolae 26-29 in 10 μm............................................................................................................................................................. F. lyra
6b Areolae 35-40 in 10 μm......................................................................................................................................................................7
7a Valves 15.5-18.5 μm long, 6.5-7 μm wide.................................................................................................................. F. christensenii
7b Valves 26-37 μm long, 8-9 μm wide............................................................................................................................... F. giffeniana
8a Striae parallel in the middle of the valve................................................................................................ F. giffeniana var. yemenitica
8b Striae radiate in the middle of the valve.......................................................................................................................... F. geisslerae
9a Valves elliptic with broad apices........................................................................................................................................ F. elliptica
9b Valves with distinctively protracted apices......................................................................................................................................10
10a Striae parallel in the middle of the valve.......................................................................................................................... F. orientalis
10b Striae radiate in the middle of the valve...........................................................................................................................................11
11a Striae 12-14, Areolae 15 in 10 μm...................................................................................................................................... F. coreana
11b Striae 18-21, Areolae 21-24 in 10 μm.................................................................................................................................... F. densa