. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology. Fig. 5. Harpillaenus arcuatus (Billings). Restoration suggesting com- plete exoskeleton may have eleven thoracic segments, exact number un- knoA\ni. A, dorsal view: B, right lateial view; c. X 2. Compare Plate 20, figures 15, 16; Plate 21, figures 1, 2, 6, 7, 11, 13. ventral exoskeleton is not well known in this group, and the dorsal exoskeletal characters of Harpillaenus are not outside the range of known illaeninids. In the form of the rostral plate, as well as other characters, Harpillaenus does not resemble such O
. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology. Fig. 5. Harpillaenus arcuatus (Billings). Restoration suggesting com- plete exoskeleton may have eleven thoracic segments, exact number un- knoA\ni. A, dorsal view: B, right lateial view; c. X 2. Compare Plate 20, figures 15, 16; Plate 21, figures 1, 2, 6, 7, 11, 13. ventral exoskeleton is not well known in this group, and the dorsal exoskeletal characters of Harpillaenus are not outside the range of known illaeninids. In the form of the rostral plate, as well as other characters, Harpillaenus does not resemble such Ordovician bumastinids as Dijsplanus, Platillaenus (Jaanusson, 1954; in Moore, 1959) or Buniastoides (Whittington, 1954, pp. 138-139, pi. 62, figs. 16-18, 20, 25, 26, 29). There is some resemblance between Harpillaenus and the Upper Ordovician ectillaeninid Zdicella (Snajdr, 1957, pp. 225-232, pi. 5, figs. 1-6; text-figs. 29, 30). This latter genus lacks eye lobes, but is characterised by the narrow axis, genal prolongations, and the entire margin of the inner edge of the pygidial doublure. The rostral plate of Zdicella is trapezoidal in outline, situated on the gently convex ventral doublure, the connective sutures not displaying a strong curvature which is concave outwards. The resemblances between the two genera may be an example of homeomorphy rather than an indication of Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Harvard University. Museum of Comparative Zoology. Cambridge, Mass. : The Museum
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