Eatoniella fuscosubucula is a species of marine gastropod mollusc in the family Eatoniellidae. First described by Winston Ponder in 1965, it is endemic to New Zealand, found low tide and moderately deep water around the southern South Island, Stewart Island, the Auckland Islands, and around Hicks Bay in the eastern North Island.
In the original description, Ponder described the species as follows:
The species measures by . It can be distinguished from E. dilatata due to its colour and larger size, and from E. verecunda due to its smaller size, larger aperture, thinner shell and brown inner layer.
The species was first described by Winston Ponder in 1965, who used the name Eatoniella (Dardanula) fuscosubucula. The modern convention of formatting of the name without a subgenus (as Eatoniella fuscosubucula) was established by Hamish Spencer and Richard C. Willan in 1995. The holotype was collected by Elsie C. Smith in January 1950 from Paterson Inlet, Stewart Island. It is held by the Auckland War Memorial Museum.
The species is endemic to New Zealand, found in southern South Island, Stewart Island, the Auckland Islands, and around Hicks Bay in the eastern North Island. The species is found in low tide to moderately deep water, ranging in depths between below sea level.