Page:Walcott Cambrian Geology and Paleontology II.djvu/151

NO. 4 this they extend downward and with a gentle outward curve across the frontal limb and then curve inward across the broad frontal margin. Cranidium with a rather large, subconical, moderately convex glabella that shows very slight traces of lateral furrows. Occipital ring separated from the glabella by a furrow that is rather shallow and nearly transverse; occipital ring slightly convex and of nearly uniform width. Fixed cheeks narrow, about one-fourth or less of the width of the glabella; posteriorly they merge into the large subtriangular postero-lateral limbs which are marked by a shallow, intermarginal posterior furrow; anteriorly the fixed cheeks pass gently down and merge into the frontal limb. Palpebral lobe small, less than one-fifth the length of the cephalon; it is continued in a low ridge diagonally across the fixed cheek to the antero-lateral margin of the glabella. Frontal limb less than one-half the width of the broad, gently convex, frontal border; in front of the glabella it slopes gently downward to a shallow furrow that serves to distinguish it from the frontal border. Free cheeks unknown.

Thorax with twelve rather narrow, slightly convex segments with pleural lobes that arch slightly backward; axial lobe of each segment moderately convex and unmarked, so far as known, by any tubercles or spines; at a clearly defined dorsal furrow it unites with the pleural lobe which is about one-third wider than the axial lobe; the pleural furrows originate at the anterior inner side of the pleural segment and extend outward subparallel to the anterior margin about one-half the length of the pleural portion of the segment; the deepest portion of the furrow is just within the narrow anterior border which is about one-fourth the width of the segment; the exterior half of the segment is gently convex and terminates in a rather bluntly rounded end which may possibly be continued backward as a very short spine or point.

Pygidium large, moderately convex, with a short, convex axial lobe and very broad, campanulate margin; axial lobe about one-half the length of the pygidium, marked by two shallow, transverse furrows that are continued out on the gentle downward slope of the pleural lobes, outlining two segments marked by short, shallow, narrow furrows; the outer portions of the pleural lobes are nearly flat or rising slightly toward the postero-lateral margins; the semicircular outline of the pygidium is interrupted toward the median axis by a slight inward curvature.

Surface slightly roughened, but not pitted or punctate so far as can be determined. The outer half of each pleura is marked by