You're leaving out a subparagraph header.  The citation should be:

Section 1341(a)(5)(B) 

Most of the time federal statutes are number, letter, number, letter.  First ulc, then caps.  Then I think they get into Roman numerals, but I would have to look for one to be sure. 

The reference to the 1939 Code is in artifact from 1954 (and then 1986) in case you had any years that go back that far.  Ignore it.