Amphithrix amoena Kützing, 1843b: 220 (type locality: Nordhausen, Germany).
Phormidium ambiguum Gomont, 1892b: 178–179, pl. 5: fig. 10 (including Indian Ocean record).—Krishna Pillai, 1955b: 22.— Farghaly, 1980: 137.— Lambert, Steinke, & Naidoo, 1989: 487, fig. 22, tables 2, 3.— G. Subramanian et al., 1989: 320.— Thajuddin & G. Subramanian, 1992a: table III.
INDIAN OCEAN DISTRIBUTION: India, Madagascar, South Africa, Sri Lanka.
Note: Phormidium ambiguum was proposed as a substitute name for Amphithrix amoena Kützing in consideration of the prior existence of P. amoenum Kützing (1843b: 192; type locality: not specified). Drouet (1968: 232, 246), after examining the holotype of A. amoena (in L), assigned it to Microcoleus vaginatus (Vaucher) Gomont.