\begin{table}%t7
%\centering
\par
\caption{\label{tab:opticalref}References for Table~\ref{tab:clusters}.}
\begin{tabular}{l l l l}
\hline\hline\noalign{\smallskip}
{Symbol}     &    {Reference}       & {Symbol}     &      {Reference}  \\
\hline
62       &    \citet{Geller1984}        &77     &   \citet{Wu1995}          \\
63       &    \citet{Chernomordik1995}  &78     &   \citet{Condon1990}      \\
64       &    \citet{West1991}          &79     &   \citet{Kim1991}         \\
65       &    \citet{Dobrzycki2002}     &80     &   \citet{ODea1996}        \\
66       &    \citet{Edge1995}          &81     &   \citet{Hintzen1984}     \\
67       &    \citet{Ryle1968}          &82     &   \citet{Nair1997}        \\
68       &    \citet{Cristiani1997}     &83     &   \citet{White1999}       \\
69       &    \citet{Zwicky1966}        &84     &   \citet{Golev1998}       \\
70       &    \citet{Lipovka2002}       &85     &   \citet{Smail2003}       \\
71      &    \citet{Ledlow1995}         &86     &   \citet{Hintzen1983}     \\
72      &    \citet{Zwicky1968}         &87     &   \citet{Andernach1988}   \\
73      &    \citet{Tyson1986}          &88     &   \citet{Hutchings1998}   \\
74      &    \citet{Dunn2005}           &89     &   \citet{Miller2002}      \\
75      &    \citet{Hill1991}           &90     &   \citet{Gehren1984}      \\
76      &    \citet{Maoz1995}           &       &                           \\
\hline
\end{tabular}
\vspace*{-2.5mm}
\end{table}