A Napoleonic (or just a tad earlier), probably naval dirk. The dark grip generally regarded for a junior officer. The pommel likely what is regarded a "pillow" pommel. Possibly German manufacture but often British use. I'd like to see the blade decoration, point of the blade ^^^^^^up.
Cheers
GC
Edit to add a sold example with a diamond cross section blade.
http://steverogersantiques.com/cgi-b...tem_id=170214a