Strange clef

[Erik Sandberg]

Hi,

I am typesetting some Italian instrumental works from around the 1750s, and 
found something that looks and behaves like a clef, but I have never seen 
anything like it before and it is not in Lilypond's set of glyphs. Does 
anyone have a clue about what it could be?

In ASCII art, it looks something like:

 | | |
-+-+-+--\
 | | |   \
-+-+-+    |
 | | |    |
          |
          |
          |
          |
          |

where the #-ish thing in the upper-left corner looks quite much like a sharp 
sign and vertically is placed where the sharp for eis would be in bass clef 
(ie. between the second and third line from the top)

It is used in Basso Continuo parts, when the pitch is relatively high.

Erik