Fig. 3. Specimen 235. Dorsal side of the appendages of the thorax and pygidium. See pl. 7, fig. 2 for the ventral view. On pl. 9, fig. 2 (left side) is a drawing taken from the same specimen. × 11. Fig. 4. Specimen 238. Part of a thorax and pygidium, seen from the ventral side. The series of heavy segments shown in the upper part do not belong to one appendage, but are the distal ends of several endopodites. See also text fig. 46 for a drawing of this specimen. × 18. Fig. 5. Specimen 237. Pygidium and part of the thorax, with some of the appendages. × 11. PLATE VIII. HELIOTYPE CO. BOSTON * * * * * PLATE 9. _Cryptolithus tessellatus_ Green. Upper drawing by C. E. Beecher; lower drawing by Miss F. E. Isham, under the direction of C. E. Beecher. Fig. 1. Appendages of the thorax and pygidium, seen from the ventral side. These are not restorations, but drawings from the halved individual numbered 236 (right side of drawing) and 235. For photographs of these specimens, see pl. 7, figs. 2, 4. × 20. Fig. 2. Appendages of the thorax and pygidium, seen from the dorsal side. Same specimen as in fig. 1. For photographs, see pl. 7, fig. 5, and pl. 8, fig. 3. × 20. PLATE IX. HELIOTYPE CO. BOSTON * * * * * PLATE 10. From photographs made by C. E. Beecher. Fig. 1. _Isotelus latus_ Raymond. Ventral surface of the specimen in the Victoria Memorial Museum at Ottawa, Canada. Note the large, club-shaped coxopodites and the more slender endopodites. The first large coxopodite back of the hypostoma belongs to the last pair of cephalic appendages. The coxopodite of the appendage in front of it is seen turning in beneath the tip of the hypostoma. × 2. Fig. 2. _Isotelus maximus_ Locke. The ventral side of the specimen described by Mickleborough and now in the U. S. National Museum. The tips of the hypostoma may be seen at the front, and the first two pairs of coxopodites behind them belong to the last two pairs of appendages of the cephalon. Note how much stronger the coxopodites are than the endopodites. The appendages of the pygidium show but poorly, × 1.45. PLATE X. HELIOTYPE CO. BOSTON * * * * * PLATE 11. _Ceraurus pleurexanthemus_ Green. A restoration of the ventral surface and appendages, made by Doctor Elvira Wood, under the supervision of the writer, from data obtained from the translucent slices prepared and described by Doctor Walcott. × 5. PLATE XI. HELIOTYPE CO. BOSTON * * * * * Transcriber's Notes Small captioned text was not converted to ALL CAPS. The numer 1 and capital I both look alike in the printed version. Therefore, some of the volume, plate and other roman numerals may have been incorrectly converted to 1. Some tables were reformatted due to space considerations.