Dimension of a family of curves (reviewed)

Given a group of automorphisms $G$ acting on a curve $X/\C$ of genus $g$, with signature $[g_0;m_1, \ldots, m_r]$, the dimension of the family of curves with this signature is $3g_0+r-3$, where $r$ is the number of branch points of the map $X \to X/G$ and $g_0$ is the quotient genus.