Page:Walcott Cambrian Geology and Paleontology II.djvu/149

NO. 4 postero-lateral limbs, the greater part of which is taken up by the strong intermarginal furrow. Glabella without traces of transverse furrows except a short, slight indentation indicating a posterior pair of furrows; the glabella is separated from the fixed cheeks by a very narrow, strong dorsal furrow; the frontal limb is about the same width as the frontal margin, and extends almost directly downward from the dorsal furrow in front of the glabella to the sharp angle made by its union with the frontal margin; fixed cheeks about one-third the width of the glabella opposite the palpebral lobes, gently convex, and merging into the anterior and posterior limbs; occipital ring separated from the glabella by a strong rounded furrow, it is convex, broad along the center portions, and narrow toward the dorsal furrow. Palpebral lobe small, elevated, and about one-fourth the length of the cephalon; a low ridge extends from its anterior end forward and inward to the dorsal furrow beside the glabella. Free cheeks small, gently convex, and bordered by a flattened rim that is continued posteriorly into a spine; they are separated from the cranidium by the facial sutures which cut the posterior margin a short distance within the genal angles and extend with a slight sigmoid curve inward and forward to the base of the palpebral lobes; curving around these they extend with a slight outward curvature to the angle formed by the union of the frontal limb and margin, and then curve slightly inward across the margin.

Thorax with twelve rather narrow, nearly transverse segments; axial lobe convex, with the segments slightly rounded and separated from the pleural lobes by the obtuse angle formed by the union of the two lobes; pleural lobes a little wider than the axial lobe and flattened for about half their width, or to the geniculation, where each segment curves downward and slightly backward; pleural furrow relatively broad; it starts near the inner anterior edge of the pleural segment and extends along the center of the segment to the geniculation, where it gradually narrows to a point near the end of the flattened falcate termination of the segment.

Pygidium small; the subconical convex axis is marked by three shallow transverse furrows that outline three rings, and a terminal section that terminates within a short distance of the posterior margin of the pygidium; pleural lobes marked by the extension of the transverse furrows on the axial lobe and the faintly indicated, rather narrow border.

Surface slightly roughened by shallow pits or a network of very minute, irregular ridges, the interspaces of which give a pitted appearance.