Extract from metalink
Begining of Oracle 8.1 oracle eliminates SNAP$_, MVIEW$_ and the VIEW that was the snapshot.
As of 8.1, Oracle creates the base table which IS the snapshot. This base table will have the name that you have specified during the create snapshot process.
The index I_SNAP$_ is still created but now corresponds
to the primary key (if snapshot was created with primary key, which is default) OR corresponds to the HIDDEN rowid column M_ROW$$ (if snapshot was created with rowid)."
RTD: Oracle Replication