Internal moulds of complete shells, including conch and associated opercula, of the hyolith 'Triplicatella disdoma' from Cambrian Series 2, Stages 3-4 of South Australia are described. The conch of 'T. disdoma' is shown to be narrow and cone-shaped, and with a rounded triangular cross-section. The conch shows a gentle dorsal curvature in lateral view. The fossils lack evidence of helens, and the operculum was smaller than the apertural diameter of the conch and could be withdrawn a short distance into the conch. 'Triplicatella' was probably closely related to orthothecid hyoliths.