Dismal days

From the Latin dies mali, literally “evil days”.

January 1 and 25
February 4 and 26
March 1 and 28
April 10 and 20
May 3 and 25
June 10 and 16
July 13 and 22
August 1 and 30
September 3 and 21
October 3 and 22
November 5 and 28
December 7 and 22