Ninety-nine days. That is how little time remains until a Dec. 8 special primary election in Massachusetts that will precede a Jan. 19, 2010, special general election, scheduled Monday by Democratic Gov. Deval L. Patrick to determine a successor for Edward M. Kennedy.

If that sounds like a compressed schedule to elect a senator, well, that’s because it is. In most states, special Senate elections are held in November of even-numbered years, regardless of when the vacancies occurred.

The speedy time frame for the Massachusetts contest (where the Dec. 8 Democratic primary is the key election in the strongly Democratic state) piqued my curiosity about other shotgun Senate special elections.