Subonoba inornata is a species of sea snail, a marine gastropod mollusc in the family Rissoidae. It is endemic to New Zealand, found in the southern South Island, the Chatham Islands, Snares Islands and Stewart Island.
In the original description, Powell described the species as follows:
The shells of the species measure in height and in diameter. It can be differentiated from S. parvula due to its larger size, shouldered appearance and by having fewer spiral lirae, and identified due to its distinctly D-shaped large aperture.
The species was first described by A. W. B. Powell in 1933. In 1995, Hamish Spencer and Richard C. Willan recombined the species as Onoba inornata. While this remains the preferred name by the New Zealand Organisms Register, the original combination, S. inornata, is the preferred name by the World Register of Marine Species and The Marine Biota of Aotearoa New Zealand (2023). The holotype was collected by Powell himself in February 1933, from seaweed at Waitangi in the Chatham Islands, and is held by the Auckland War Memorial Museum.
S. inornata is endemic to New Zealand, found in the waters surrounding the South Island as far north as Banks Peninsula, Stewart Island, Snares Islands and the Chatham Islands, at depths between . Previously, the species was thought to be endemic to the Chatham Islands.