Consulted a couple of books on these: Tracking and the Art of Seeing by photographer and writer Paul Rezendes, who lives in Western MA, and Mammal Tracks and Sign of the Northeast, by Diane K. Gibbons, a naturalist and illustrator who makes her home in Southern NH. Looks like they’re the front paws of a muskrat, which makes sense as we’re about a half mile from where the CT River flows into the Long Island Sound, with plenty of shallow wetlands in the area for food and shelter.