Here's the breakdown:
3 GOP Senators retiring outright
1 Dem Senator (and that was Franken)
24 GOP Representatives retiring outright
1 Dem Rep retiring outright
11 GOP Representatives running for higher office
4 Dems Reps running for higher office
(the 'higher office' is either the Senate or a Governorship)
So in the House there are 35 GOP Reps who are NOT running for re-election and 5 Dems.
On average 22 Representatives (total of both parties) retire per election cycle. If you split it down the middle, that means that on average 11 GOP Reps retire at the end of an election cycle. There are 35! Sounds either like rats deserting a sinking ship or "May I be excused from the trough, I've gorged myself long enough, thank you".