Thanks Malte, that was stupid of me. Improved MWE below.
Andrew, this is just a shortcut in notation, developed when scores had to be handwritten. Writing it this way (as in bars 1 and 2) is a lot easier than the long version (bars 3 and 4). It doesn't seem to be used much in modern scores but was very prevalent in the the 1800s and earlier. When you see it in context you'd have no problem interpreting it.
All the best,
Craig
\version "2.19.82"
\language "english"
notes = \relative c'' {
%1
\tuplet 3/2 2 { g2.:8 a2.:8 } |
%2
\tuplet 3/2 2 { bf2.:8 bf2.:8 } |
%3
\tuplet 3/2 4 { g8 g g g g g a a a a a a } |
%4
\tuplet 3/2 4 { bf8 bf bf bf bf bf bf bf bf bf bf bf } |
}
\score {
\new Staff
\notes
\layout { }
}