You could say the sixth is an infinitely large one made of regular hexagons.
(Polyhedronal duality: Surface midpoints are vertices of the dual. Ex: The six surface midpoints of a cube are the six vertices of a regular octahedron; and vice versa.)
for each of these, working out
1/s + 1/m - 1/2 = 1/E
gives 1/E = 0
... which makes sense (kind of) since those
three cases are infinite regular tilings instead of regular polyhedra ...(EDIT: Just noticed jonsen's comment here too, "infinihedron" suddenly makes sense to me :-) )