Today's mystery object.

I bought this dagger and sheath made from leather and snakeskin in an Inverness antique (junk?) shop back in 1966.
I have never managed to discover from whence it came. I would be more than delighted if anyone can throw any light on its origin. 

PS. Thanks to Shutterup and others I now know that it is a Sudanese Mahdi Dervish Arm Dagger  - c.1885. I am more than grateful!