Septaria borbonica: Shell: Length up to 23 mm, mean w/1 ratio 0.74, mean h/1 ratio 0.33. Shell symmetrical, cap-like with apex outside the posterior margin of the shell, but often eroded. Widest across the septum. Dorsal pattern is often covered by a dark encrustation. Ground colour Yellow-brown with dark lines making a pattern of small intricate triangles and/or ovals. Inside dark gray with a yellow, narrow septum. Males and females the same size and the same number of each sex in populations. Operculum: Fragile, thin, pale pink-orange and wider at the posterior. Horn margin darker pink-orange and the rib short and often knobbly or crooked.

Septaria borbonica: Septaria borbonica and Septaria porcellana have been confused by many authors. Although the shells of the two species are somewhat similar, S. borbonica’s shell is flatter and more shovel-shaped and its anatomy and geographic distribution is different as S. borbonica is confined to the Indian Ocean. I have collected it from Mauritius and Seychelles, while STARMUHLNER found it in Madagascar (1969), Comoros, Rodriguez and Reunion (1983). The Natal Museum has specimens collected from Transkei and Zululand on the Kwazulu Natal coast. BENTHEM-JUTTING (1956) mistakenly called S. cumingiana from Java S. borbonica (Figures of shell and operculum show this). Confusion between S. borbonica and S. porcellana began when RECLUZ (1841) com¬bined the two species. As he correctly stated, BOURNE (1908) studied the anatomy of S. borbonica and not that of S. porcellana. RIECH (1937) and STARMUHLNER (1970) used the name S. borbonica depressa when referring to the New Guinea and New Caledonian S. porcellana.

Septaria borbonica: Range: Indian Ocean Islands - Seychelles, Mauritius, Rodriguez, Reunion, Comoros, Madagascar, East Coast of Africa e.g. Kwazulu Natal. In still and swift water on stones and rocks from a few metres from the sea to 4 - 5 km inland.