  Skeletal signatures were introduced in [J W Anderson and A Wootton, A Lower
Bound for the Number of Group Actions on a Compact Riemann Surface, Algebr.
Geom. Topol. 12 (2012) 19--35.] as a tool to describe the space of all
signatures with which a group can act on a surface of genus $\sigma \geq 2$. In
the present paper we provide a complete description of the gaps that appear in
the space of skeletal signatures, together with proofs of the conjectures posed
in our earlier work.
