  Extensive air showers of cosmic rays with energies above 5.10**18 eV
registered by the Yakutsk array have been analyzed. The existence of showers
without muon component is found. Among them we found 5 clusters and these
clusters correlate with nearest pulsars. It is found that there exist 4 classes
of showers. Showers with high content of muons are mainly observed at E>
4.10**19 eV and they are formed most likely by heavy nuclei.
