Sebastopol is a Block game because there is no boneyard.
Four play. Each draws seven bones. The 6-6 must bet set, and the turn then rotates to the left of the first player. The 6-6 is open four ways, and the first four plays after the set must be upon it - no branches may be extended until all four have sprouted. In all other respected, the rules are those of the "Block" game.