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The type species of the assimineid genus Acmella W.T. Blanford, 1869 is Cyclostoma tersum Benson, 1853, originally described from 'Musmai' [Mawsmai], Meghalaya, Northeast India. No specimens from Benson's type series can be traced, and contemporary shells collected from the type locality in museum collections are extremely worn. It has therefore been impossible to examine shell microsculpture, an important taxonomic character in the diagnosis of species of Assimineidae, using museum specimens. In order to provide better diagnostic characters for the genus Acmella, we redescribe and illustrate Acmella tersa from newly collected specimens, one of which is designated as the neotype. We also provide a list of all known species attributed to Acmella.