In a version of "Overture to Lucio Silla" by Mozart, half of the viola part of the song has half notes with a SINGLE slash through it, but 4 dots on the base part of every not (The circular part). Right before it in many cases, there are 4 eighth notes in which all have a single dot for staccato.
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The slash symbol through the stem of a note is called a "tremolo" notation, and signals that the same pitch or chord is to be repeated at a certain rate. In your example, it is a shorthand for eighth notes. The half note signifies the length of time the notes will fill (in this case two beats). The stem plus the dots shows the division.
Here is a good example of how this can be useful practically, from a flute method book.
As Reina pointed out, the slash is a kind of an abbreviated beam, indicating, that the note has to be played as repeated eigth notes (two slashes/beams would indicate 16th etc.). The dots are most likely the staccato dots for the resulting four eights, so nothing changes in comparison to the previous bars.
There is a difference between a single slash and the several slashes for a tremolo. A half note with a slash through it in this case with the four dots underneath, is a shorthand meaning that you play four notes for each one written. So if you have half notes written and four dots then you play eighth notes.
