a1 Department of Mathematics, University of Aberdeen, The Edward Wright Building, Dunbar Street. Aberdeen, AB9 2TY.
a2 Department of Mathematics, The Ohio State University, 231 West 18th Avenue Columbus, Ohio, 43210-1174, U.S.A..
Introduction. Polyhedra in 3-dimensional hyperbolic space which give rise to discrete groups generated by reflections in their faces have been investigated in , ,  and in the case of tetrahedra there are precisely nine compact non-congruent ones with dihedral angles integral submultiples of π . These polyhedral groups give rise to hyperbolic 3-orbifolds and examples of these have been studied, for example, in , , , , .
(Received January 13 1989)