Rich: Your dagger is a tebu - or toubou, depending on how you represent it - dagger from the Sahara desert. Please refer to these old threads for more information on this style:
Tebu dagger from Goa
Toubou knife for your comment, from Chuck
Lew: I find it interesting that your most recently pictured dagger has the same device on the forte of the blade as mine that was pictured in the thread you cited in the same post. This style is attributed specifically to Sudan the country, as in Khartoum, while Rick's knife is from further west in the Sahara (Chad, Niger), a product of an oasis dwelling people.