Page:Walcott Cambrian Geology and Paleontology I.djvu/34

16 transverse except at the axial lobe, where it arches slightly forward; the slope from the central portion of the cephalon to the margin is unbroken by any furrow and there is no clearly defined or raised rim. Cranidium with a broad campanulate frontal limb that extends from the anterior base of the eyes obliquely outward and forward and directly forward from the glabella to the outer margin of the cephalon; the posterior limbs, on their inner side, occupy the space between the posterior base of the eye and the posterior margin of the cephalon and extend outward to the lateral margin with a gradually increasing width; there is no fixed cheek between the palpebral lobe and the glabella; palpebral lobe about one-third the length of the cephalon and situated a little back of the center; it is slightly elevated along the outer margin and slopes toward the dorsal furrow next to the glabella. Glabella about three-fifths the length of the cephalon; it has subparallel sides up to the front of the eyes, where the sides curve inward and unite to form an obtusely rounded outline; in front the glabella merges into the frontal limb, so as to make it difficult to indicate a line of division between them; the glabella is gently convex and more or less clearly marked by a narrow median ridge, and, on each side of the ridge, two pits that indicate transverse furrows, very much as do the pits on the glabella of Oryctocephalus ; there is no trace of an occipital furrow or segment. Free cheeks subquadrangular in outline; on their inner margin they support the visual surface of the eye and from there slope gently to the outer margin. The facial sutures cut the lateral margin of the cephalon some distance in front of the genal angle and extend wth a little backward curvature to the posterior base of the eye; after curving over the eye lobe they extend obliquely forward at an angle of about 50° to the margin.

Thorax with fourteen segments; the first is nearly transverse, but each succeeding pleural lobe bends back a little more than the one preceding it, so that the pleural lobe of the posterior segment is bent back parallel to the side of the pygidium; the central axis of the thorax is gently convex, with a low median ridge that rises into a minute node on the two anterior segments; it gradually widens from the first to the seventh segment, and then narrows a little at each segment back to the pygidium; the pleural lobes are flattened between the axial lobe and the angle where the pleuræ bend more or less backward; each pleura has a broad, shallow, direct furrow that extends from the inner end out to the backward curving portion of the pleuræ; the edge of the furrow and of the segment is marked by