FIGURE 13. Chancelloria from the Middle Cambrian Wheeler Shale, Wheeler Amphitheater, Utah (USNM 509794). A. With crossed nicols. B. Red channel. C. Green channel. D. Image obtained by subtracting the pixel values of C from those of B, using the Adobe Photoshop “Difference” blending mode, adjusting the levels of the B channel for optimal contrast, and subsequently adjusting the levels in the combined channel. (Click on the picture to toggle between different views, or select one of the following links: A, B, C, D.)