Papua New Guinea Bone Dagger ?

[drac2k]

I am not very familiar with these, however, this one is even a little more unusual in the fact that it has a clay mask, feathers, hemp, and cowrie shells. It is concave in the back, so I definitely think it is bone. It is 19" long.
Any comments about the nature or significance(ancestor worship ?), of this item, would be appreciated.