Mendis is currently preparing for the World Cup with Sri Lanka
Somerset have signed Sri Lanka spinner Ajantha Mendis for the first few weeks of the County Championship season.
The off-spinner, 25, will act as cover for fellow spinner Murali Kartik while he is at the Indian Premier League.
Mendis has played in 15 Tests and 46 one-day internationals for Sri Lanka, taking 107 wickets in the process.
Somerset have also confirmed that West Indies all-rounder Kieron Pollard, 23, will return for the second half of the club's Twenty20 campaign this summer.
Mendis will join up with Somerset ahead of the start of their Championship campaign at home to Warwickshire on 14 April.
Somerset's director of cricket Brian Rose told the club's website: "We have said we would only bring in a top class performer as a replacement for Kartik if we could get one and feel that Mendis fits into that category so we are absolutely delighted about it."
Kartik was a revelation in his first season at the County Ground, taking 78 wickets in total last summer, and the addition of Mendis will boost the county's hope of claiming their first ever title, having missed out by the narrowest of margins to Nottinghamshire in 2010.
I believe Somerset can win the FP t20 this year and I will be doing my best to make that happen
Crowd favourite Pollard's return in the T20 will also be celebrated by Somerset's fans after his match-winning performances in 2010.
The Trinidadian made a real impression on the club with his all-round game, although it was his big hitting which became his trademark.
Pollard told the club website: "I believe Somerset can win the FP t20 this year and I will be doing my best to make that happen."
He scored a total of 354 runs, took 29 wickets and pulled off a match-winning catch in the T20 semi-final victory over Nottinghamshire at the Rose Bowl.
However, he had to retire hurt in the final after being floored by a bouncer from Hampshire's Dominic Cork, which left him with a severely swollen eye and forced him to go to hospital. He was unable to take the field or bowl in Hampshire's innings as
Somerset were beaten in dramatic fashion off the last ball of the game.
Pollard is likely to miss the first half of Somerset's 2011 T20 campaign as he will be playing for West Indies against India in their one-day series.