\begin{center}
\footnotesize
\setlength{\mylength}{\baselineskip}
\begin{longtable}{rp{0ex}p{9cm}p{0ex}RL}
\caption{Laurent polynomials and selected mutations for bucket 15.}\\

\toprule \multicolumn{1}{c}{{Node}}&& \multicolumn{1}{c}{{Laurent polynomial}} && \multicolumn{2}{c}{{Mutations from Figure~\ref{fig:15a}}} \\ \midrule \endfirsthead

\multicolumn{6}{c}{{\tablename\ \thetable{} -- continued from previous page}} \\ \addlinespace[1.7ex] \midrule \multicolumn{1}{c}{{Node}}&& \multicolumn{1}{c}{{Laurent polynomial}} && \multicolumn{2}{c}{{Mutations from Figure~\ref{fig:15a}}} \\ \midrule \endhead

\midrule \multicolumn{6}{c}{{Continued on next page}} \endfoot

\bottomrule \endlastfoot

21 && $x+\frac{x}{y}+y+z+\frac{1}{yz}+\frac{1}{x}$ && $70 \colon {}$ & $\left(\frac{xy}{y+1},\frac{x}{y+1},z(y+1)\right)$ \bottomspacer \\ \addlinespace[1.1ex]
 \rowcolor[gray]{0.95}
46 && $x+y+z+\frac{z}{y}+\frac{1}{x}+\frac{2}{xy}+\frac{1}{x^2yz}$ && $70 \colon {}$ & $\left(x,\frac{xyz+1}{xz},yz\right)$ \bottomspacer \\ \addlinespace[1.1ex]
 70 && $x+yz+y+z+\frac{1}{x}+\frac{1}{xz}+\frac{1}{xy}$ && $21 \colon {}$ & $\left(x+y,\frac{x}{y},\frac{yz}{x+y}\right)$ \spacer \\* 
 &&  && $46 \colon {}$ & $\left(x,\frac{xyz}{xz+1},\frac{xz+1}{xy}\right)$ \bottomspacer \\ \addlinespace[1.1ex]
 \end{longtable}
\end{center}
