I found this symbol under this link in the piece "Geistliche Chormusik" Nr. 22 of Heinrich Schütz. I have highlighted the symbol in the middle voice where it appears twice.
The highlighted symbols are breve noteheads.
Each lasts for eight beats - twice as long as a four-beat semibreve.
And they have pitch. In your example, the lower voice on the middle stave plays an E natural breve followed by a D semibreve. The upper voice has crotchet rest, G sharp minim, G sharp crotchet then an A natural breve.