Key 1: Key to Ilanga species of south-western Indian Ocean studied

1. depressed spire (height to width ratio <= 0.6)............................................. I. discus

- rather elevated spire................................................................................... 2

2 (1). subsutural axial pleats visible on second or third whorl.................................. I. biradiatula

- no obvious subsutural axial pleats on whorls............................................................... 3

3 (2). rounded periphery, convex whorls, strong spiral cords on first whorl.......................... I. herberti

- subangulate periphery, very weak spiral cords on first whorl.............................. I. laevissima