County champions Essex begin the defence of their title in 2018 against Yorkshire at Headingley on 13 April.
Northamptonshire sign Lancashire all-rounder Luke Procter on a three-year deal starting from next season.
Northamptonshire all-rounder Rob Keogh signs a new contract to stay with the club until the end of the 2019 season.
Seam bowler Brett Hutton is to leave promoted Nottinghamshire and join Northants on a three-year contract.
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Watch highlights of Adam Lyth's 161 as he breaks the domestic record in Twenty20 cricket as Yorkshire make 260-4 against Northants to amass the highest domestic T20 score.
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