Allenby and Meschede in swap deal
Allenby signed a four-year deal with Glamorgan only 12-months ago but has negotiated his release and will strengthen a Somerset side recently weakened by the departure of Nick Compton.
Allenby has a superb all-round record in Division Two of the County Championship, with a batting average in excess of 40 and a bowling average below 26. He scored more than 900 first-class runs last year and claimed 52 Championship wickets. He has been Glamorgan's leading run-scorer in the Championship for the last two years and topped the side's T20 batting averages and wicket-takers list. This will be the first time in his career he has played Division One cricket.
"I have enjoyed my time at Glamorgan and I would like to thank the supporters for welcoming me to Wales and for all the support whilst I have played for the club," Allenby, who joined the club in 2009, said. "I leave Glamorgan with some great memories and what I hope will be life-long friendships. I wish the players every success and hope they have long and enjoyable careers."
The move will reunite Allenby with his former coach at Glamorgan, Matt Maynard, who was recently appointed director of cricket at Somerset and alleviates the disappointment caused by Nick Compton's departure to Middlesex.
Maynard said: "I am delighted that Jim is joining us. Not only is he an outstanding player in all formats, he is a great bloke and a strong character and I am sure he will play a key part in helping us to build a cohesive and successful team. Whilst not a like for like replacement for Nick Compton, there is no doubt in my mind that Jim is a superb acquisition to a very talented Somerset squad."
Meschede's opportunities might have been reduced even further with Allenby's arrival in Taunton, but his loan should assure him of more first team experience. He remains highly-rated at Taunton but has struggled for first team opportunities over the last couple of years.
"Craig has been brilliant in recognising that a loan to Glamorgan will enable him to play more first team matches than was likely at Somerset next season," Maynard said. "The maturity and enthusiasm which he has displayed since I raised the possibility of a loan move with him has been heartening and I am sure he will grow in stature and experience during the 2015 season."
Glamorgan have also announced that Jacques Rudolph has extended his deal until the end of the 2017 season.
"Whilst we appreciate the on-field contribution Jim has made to Glamorgan County Cricket Club over the past five seasons, we are disappointed he feels the next stage of his career would be best served away from the SWALEC Stadium," Glamorgan's chief executive Hugh Morris said.
"It is a shame to see Jim depart, but as we are focused on rebuilding a team capable of consistently competing for domestic honours, we need to have everyone at the club fully committed to bringing success back to the county."
George Dobell is a senior correspondent at ESPNcricinfo