On shell discs from the mounds of Tennessee the rattlesnake is so represented (fig. 131). The head of the rattlesnake with upturned upper jaw is readily recognized in fig. 131 _a_. Behind the mouth, the eye represented by a number of circles, will be seen. The body continues along the lower rim towards the right and terminates on the left, in a rattle. The analogy between fig. _b_ and _a_ is easily recognized; the essential difference consists in the fact that the body in _b_ is undecorated; the rattle lies just over and behind the eye. Figure _c_ still preserves the same form, but added to the decorations found in the preceding specimens, is the long loop with small circles surrounding the eye. The position in _d_ is slightly changed; the eye will be easily recognized and just to the right of it, more upright than in the preceding specimens, is the mouth with a fang. The body is in the same position as before, following the rim of the disk and ending in a rattle. In _e_ the mouth is very much shortened and the eye is reduced to a single small circle, while the body and tail retain their characteristic features. [Illustration: Fig. 131. Shell with representation of rattle snake.] The formal elements which were discussed in the beginning of this book exert a far-reaching influence upon decorative forms. The exigencies of symmetry within a decorative field require adjustments which may modify the representative form considerably. A peculiar effect of inverted symmetry may be seen in those Borneo shields in which the whole shield represents the face of a demon; one half to the left of the vertical middle line right side up, the other half upside down.[85] [85] A. R. Hein, Die bildende Künste bei den Dayaks of Borneo, figs. 48, 49, 51.