\begin{table}%t10
\caption{Mean differences in the Lick indices at a given $\sigma$ between
galaxies in different environments.  For each index, we list the mean offset
$d$ and its error $\Delta d$ and the $t$-parameter (of the statistical test
$d\ne 0$).\label{tab-differences}}
%\centering
\par
\small
\begin{tabular}{@{}l r r r@{}}
\hline\hline
Index       &  
\multicolumn{1}{c}{$d$} &
\multicolumn{1}{c}{$\Delta d$} &
\multicolumn{1}{c@{}}{$t$}\\
\hline
D4000        &$ 0.0067$ & 0.0208     & 0.321\\  
H$\delta_A$  &$ 0.0202$ & 0.0041     & 4.904\\
H$\delta_F$  &$ 0.0158$ & 0.0032     & 4.886\\
CN$_2$       &$-0.0287$ & 0.0062     & 4.600\\
Ca4227       &$-0.0057$ & 0.0034     & 1.689\\ 
G4300        &$-0.0035$ & 0.0034     & 1.121\\
H$\gamma_A$  &$ 0.0061$ & 0.0033     & 1.843\\
H$\gamma_F$  &$ 0.0060$ & 0.0042     & 1.442\\
Fe4383       &$-0.0029$ & 0.0022     & 1.332\\ 
Ca4455       &$-0.0063$ & 0.0020     & 3.166\\
Fe4531       &$-0.0058$ & 0.0015     & 3.827\\  
C4668        &$-0.0103$ & 0.0029     & 3.535\\
H$\beta$     &$ 0.0006$ & 0.0024     & 0.259\\
Fe5015       &$-0.0053$ & 0.0014     & 3.776\\
Mgb          &$ 0.0015$ & 0.0029     & 0.500\\
Fe5270       &$-0.0022$ & 0.0010     & 2.146\\ 
Fe5335       &$ 0.0014$ & 0.0014     & 0.993\\
\hline
\end{tabular}
\end{table}