Key to the identification of American species of the costata -group

1 Distal angle of postabdomen projected and acute, slightly narrowed distally. Lateral head pores long, over 1/2 IP................................................................................................ 2 (costata- branch)

- Distal angle of postabdomen rounded and projected, strongly narrowed distally. Lateral head pores short, about 1/3 IP............................................................................................ 3 (rustica- branch)

2 Three main head pores........................................................... Alona margipluma sp. nov.

- Two main head pores.......................................................... Alona cf. setigera Brehm, 1931

3 Rostrum elongated, labral keel with projections on its upper half........................... Alona bicolor (Frey, 1965)

- Rostrum not elongated, labral keel without projections........................................................ 4

4 Middle main head pore at similar distance of anterior and posterior head pore................... Alona rustica Scott, 1895

- Middle main head pore near to posterior head pore........................................................... 5

5 Second seta on the exopodite of limb V slightly longer than first seta.............. Alona iheringula Kotov & Sinev, 2004

- Second seta on the exopodite of limb V about two times shorter than first seta................. Alona hudeci Sinev, 1999