  We report a measurement of the energy spectrum of cosmic rays above
$2.5{\times} 10^{18}$ eV based on $215,030$ events. New results are presented:
at about $1.3{\times} 10^{19}$ eV, the spectral index changes from $2.51 \pm
0.03 \textrm{ (stat.)} \pm 0.05 \textrm{ (sys.)}$ to $3.05 \pm 0.05 \textrm{
(stat.)}\pm 0.10\textrm{ (sys.)}$, evolving to $5.1\pm0.3\textrm{ (stat.)} \pm
0.1\textrm{ (sys.)}$ beyond $5{\times} 10^{19}$ eV, while no significant
dependence of spectral features on the declination is seen in the accessible
range. These features of the spectrum can be reproduced in models with
energy-dependent mass composition. The energy density in cosmic rays above
$5{\times} 10^{18}$ eV is $(5.66 \pm 0.03 \textrm{ (stat.)} \pm 1.40 \textrm{
(sys.)} ) {\times} 10^{53}~$erg Mpc$^{-3}$.
