Much larger than typical scarabs, they were placed over the heart or throat of the mummy and sometimes had a passage from the Book of the Dead carved in the underside. That passage contains instructions to help the deceased person's heart pass the weighing test (see Ma'at and the weighing of the heart). An interesting article about heart scarabs plus a spectacular example: http://archaeologicalmuseum.jhu.edu...tories/ancient-egyptian-amulets/heart-scarab/
