Shell length up to 25 mm , mean w/1 ratio 0.75, mean h/1 ratio 0.32. Shell ovate relatively narrow, with a large protruding apex but it is nearly always eroded. Ground colour yellow-green or yellow-brown with a pattern of black lines in wide triangles formed from lines radiating from the apex and crossing one another. Interior white-gray, muscle scars prominent but narrow. S. macrocephala is a protandrous sequential hermaphrodite. Males are less then 15 mm long and females are never less than 12 mm long and there are fewer males in populations. Operculum: White-pink, squarish with a narrow rib and yellow-orange to black posterior horn margin.

S. macrocephala (RECLUZ, 1841) and S. sanguisuga (REEVE, 1856) were combined under the older name by MARTENS (1881) and the two species have been confused often since then because both have a large protruding apex. S. macrocephala can be distinguished by the obvious pattern of radiating lines forming large triangles, its strongly eroded apex, its greater width across the apex and an operculum that has only one rib. It is not as easy to distinguish S. macrocephala from S. bougainvillei as both have shells that erode at the apex and an operculum with one rib. However, the pattern on S. bougainvillei shells consist of transverse or horizontal lines while the lines on S. macrocephala shells tend to radiate downwards from the summit. Both species are present in fast flowing streams on high Fijian islands. S. macrocephala has also been mistaken for female S. suffreni and the spermatophores claimed to have been from S. macrocephala by HAYNES & WAWRA (1989) are those from S. suffreni. The error was corrected in HAYNES (1991) when it was established that S. macrocephala has no spermatophores. The small males are most often found clinging to the shells of larger females.

Range: Fiji, New Caledonia, Samoa. In swift flowing streams on stones and rocks well above the influence of the sea.