Key to all known species of Sundagrapha

1 Apex of the valve quite long.................................................................... S. lepidata

- Apex of the valve short................................................................................. 2

2 Costal process slightly longer; apex of the valve flat-tipped............................................ S. laoensis

- Costal process slightly shorter; apex of the valve pointed...................................................... 3

3 Smaller in body size; distal edge of the valve concave............................................... S. tenebrosa

- Larger in body size; distal edge of the valve straight.............................................. S. recta sp. nov.