There are turtle patterns on the back of the turtle. The middle of the turtle pattern represents the three talents of heaven and earth, and at the same time represents the twenty-four mountains next to it, and there are also ten squares representing the ten-day dry. There are twelve squares at the bottom of the tortoise shell, representing the twelve earthly branches. The layout of a turtle shell actually contains all the secrets of the universe, so the turtle is regarded as one of the four spirits. Turtle was called Xuanwu in ancient times, and it was called "Four Spirit Culture" together with Qinglong, White Tiger and Suzaku.