Found description in a book, Ulu is described as a semi-lunar shaped implement mainly used by NA woman to process food, sometimes called a "squaw's knife", can be made of stone with ground edge, bone or metal
This link will tell you much regarding the types and uses of ulus. A similar tool is used to the present day by the eskimos, and it is the eskimos who refer to them sometimes as "squaw knives". the word ulu itself is an eskimo word for this type of knife. They are found mostly in the far Northeastern states and maritime Canada. Slate was the most common material used. In the Northeast, these knives are technically known as "semi-lunar knives", but collectors hereabouts still call them ulus. At any rate, there are many figures at this link allowing you to see the different styles:
flintmel, the one you found is called a comb-back ulu after the raised ridge on the top as seen in your photo, the end opposite the honed blade. It is broken some on the right hand side, but a very rare find nonetheless. Here is a slate comb-back ulu from my own collection, and found many years ago in Ma.
First pic here is the honed edge of the above Ma. comb-back ulu. Second pic is a very large broken Rhode Island example with a very pronounced comb-back. Attractive slate was often selected for these tools. These semi-lunar knives generally date from the Late Archaic timeframe in the Northeastern states.
The broken RI example was probably 7+ inches wide when made, very large for the type.