Each cluster and parallel field pair was observed for 70 orbits with the Advanced Camera for Surveys Wide Field Camera (ACS/WFC) in $F435W$, $F606W$ and $F814W$, and 70 orbits with the Wide Field Camera 3 IR channel (WFC3/IR) in $F105W$, $F125W$, $F140W$ and $F160W$, achieving $5\sigma$ depths of ${\sim}29$th AB magnitude [@lotz2017].

Despite the ${\sim}6\arcmin$ separations between the cluster and parallel fields, the parallel fields are still either within or straddle the virial radii ($R_{200}$) of the clusters and so these images are examined for UDGs as well. To estimate the contamination of our UDG sample by background galaxies, we instead use the eXtreme Deep Field [XDF, @illingworth2013]. This is the only image of the sky that is deeper than the FFs to date, and was obtained by stacking the data from 19 different *HST* programs completed between 2002 and 2012 covering the *Hubble* Ultra Deep Field [@illingworth2013]. The XDF has ACS/WFC coverage in $F435W$, $F606W$, $F775W$, $F814W$ and $F850LP$, and WFC3/IR coverage in $F105W$, $F125W$, $F140W$ and $F160W$.

[lrrrrrrr]{} Abell 2744 & $0.308$ & 00:14:20.70 & $-$30:24:00.58 & $2.06 \pm 0.42$ & $2.35 \pm 0.16$ & 99 & $1351^{+387}_{-379}$\
Abell S1063 & $0.348$ & 22:48:43.97 & $-$44:31:51.14 & $1.88 