Shell as in Siphonorbis or Plicifusus, but the whole nepionic shell smooth (it is sculptured up to the larval whorls in other species) ; operculum coiled, paucispiral; radula, with one cusp on the rhachidian and two on each lateral tooth; ovicapsules solitary, as in Tritonofusus, (Dall.)
TYPE. FUSUS mohnii Friele.
DISTRIBUTION. Arctic North America.

In Mohnia we have included a number of bathyal and abyssal buccinids that have a more or less distinctly spirally-coiled operculum and a small initial whorl in the larval shell that increases its diameter regularly (Figs 534, 537, 540, 543). The radula has a more or less square central tooth with one or three cusps and lateral teeth with two major and 0-2 minor cusps between these.
All species we know of Mohnia are true deep-water species. They are known from the N Atlantic, the N Pacific, and the Arctic basins. In some species the spiral coiling of the operculum can be observed only in young specimens because its older parts get worn rather early in life.
We have divided Mohnia in two subgenera, Mohnia s.str. and Tacita. The species of Tacita have a more or less distinct axial sculpture in addition to spiral lines and lose the spirally-coiled part of the operculum early in life. The species of Mohnia lack axial sculpture and usually the operculum keeps the apical part throughout life.
In Mohnia we have also included some species for which we could not find a better genus, although we are not satisfied with their position here, viz. M. carolinensis, M. caelatus and M. glyptus.