Form of notice requirement: file Form I or elect Form II where market share thresholds trigger enhanced disclosure and review. Notices for proposed combinations must ordinarily be filed in Form I with requisite fee; parties may opt for Form II where combined market share exceeds specified thresholds (more than fifteen percent in similar markets or more than twenty-five percent across production chain levels). Notices must comply with Commission notes and include schedule-specific declarations for acquisitions through open offers or stock exchange transactions. The Commission may direct conversion from Form I to Form II for prima facie assessment, with fee adjustment if Form II is filed within forty-five days of that direction.