This is very speculative and I hope someone can give a more reliable answer.
At some stages in the history of printed music, printers may have only had accidentals available on lines; if an accidental was required on a space, for example low F# in treble clef, they would put it on one of the neighbouring lines instead (reference - see footnote on page 4).
Perhaps the same thing was true of clefs in your example, and the "D clef" is actually a C clef which the printer was unable to print correctly on the space below. This would make the part treble clef (presumably sounding an octave lower), which seems right. The general shape is similar to that of some variant C clefs which are relatively rare today (image).