Tlingit Turtle Shell Mask Wall Hanging Pacific Northwest Coast - unusual For Sale

Tlingit mask/wall hanging painted on a turtle shell. In 4 places, sinew (?) dangles from the bottom; 2 have some sort of hair attached (horsehair?) while the hair has fallen out from the other 2. The mask measures 15\" tall by 14\" across at the widest point. There is a wire hanger attached to the back. Please see the photos for condition details.
All I know about this piece is from a piece of paper taped to it, perhaps an old collector\'s or museum\'s note. It reads \"Tlingit Tribe, Northwest Washington/British Columbia.\"