  A number of different classes of potentially extra-terrestrial bursts of
radio emission have been observed in surveys with the Parkes 64m radio
telescope, including "Rotating Radio Transients", the "Lorimer burst" and
"perytons". Rotating Radio Transients are radio pulsars which are best
detectable in single-pulse searches. The Lorimer burst is a highly dispersed
isolated radio burst with properties suggestive of extragalactic origin.
Perytons share the frequency-swept nature of the Rotating Radio Transients and
Lorimer burst, but unlike these events appear in all thirteen beams of the
Parkes Multibeam receiver and are probably a form of peculiar radio frequency
interference. In order to constrain these and other radio source populations
further, we searched the archival Parkes Multibeam Pulsar Survey data for
events similar to any of these. We did not find any new Rotating Radio
Transients or bursts like the Lorimer burst. We did, however, discover four
peryton-like events. Similar to the perytons, these four bursts are highly
dispersed, detected in all thirteen beams of the Parkes multibeam receiver, and
have pulse widths between 20--30 ms. Unlike perytons, these bursts are not
associated with atmospheric events like rain or lightning. These facts may
indicate that lightning was not responsible for the peryton phenomenon.
Moreover, the lack of highly dispersed celestial signals is the evidence that
the Lorimer burst is unlikely to belong to a cosmological source population.
