The tweet says 31 clubs participating. 39 clubs in the EoS minus the following Scottish Cup 2018/19 participants:
Hawick, Preston, Burntisland, Coldstream, Linlithgow, LTHV (all licensed)
Bonnyrigg (East juniors winners), Tynecastle (Cup winners from this season)
Then minus Stirling Uni reserves would make it 30 clubs rather than 31 unless I've missed something?