  We present the first angle-resolved photoemission measurement on the
single-layer Hg-based cuprate, HgBa$_2$CuO$_{4+\delta}$ (Hg1201). A
quasi-particle peak in the spectrum and a kink in the band dispersion around
the diagonal of the Brillouin zone are observed, whereas no structure is
detected near the Brillouin zone boundary. To search for a material-dependent
trend among hole-doped cuprates, including Hg1201, we use a tight-binding model
to fit their Fermi surfaces. We find a positive correlation between the
$T_{c,\mathrm{max}}$ and $t'/t$, consistent with theoretical predictions.
