Entomology definition of Epistoma -is: the lower face between the mouth and
eyes: that sclerite immediately behind or above the labrum,
whether it be clypeus or an intermediate piece: in Diptera, that
part of the face between the front and the labrum; the oral
margin and an indefinite space immediately contiguous thereto and
so = peristoma: in Odonata; = clypeus: = hypostoma.