The exopodites of course furnish the chief difficulty in interpretation. Doctor Walcott finds two sets of structures attached to the coxopodite, a long, slender, spiral exopodite, and a short, broad epipodite with a fringe of long setæ. Since he has given the same interpretation for _Calymene_, _Ceraurus_, and _Acidaspis_, I have considered the question of all three together on a preceding page (p. 48), and given my reasons for regarding both structures as due to sections in different directions across setiferous exopodites. Sections like those shown in figures 11, 13, and 14 of plate 27 (1918) happen to be cut in or near the plane of the setæ of an exopodite, and so show hairs of considerable length. Such sections are, as would be expected, very few in number, while sections like those shown on figures 4, 5, 7, and 9 of plate 27, which cut the setæ more nearly at right angles, are very common. Slices which give any definite idea of the form of the shaft of the exopodite are exceedingly rare. Perhaps the most satisfactory one is No. 23 (pl. 3, fig. 3, 1881), which shows the proximal part of a long, slender, unsegmented shaft, with the bases of a number of slender setæ. The organ is not complete, as would be inferred from the published figure, but the section cuts diagonally across it, and the total length is unknown. It is directed forward, like the exopodites of Neolenus, but whether or not this is a natural position is yet to be learned. The proximal, non-setiferous portion of the exopodite is evidently at an angle with the setiferous part. Another similar exopodite is apparently shown by specimen 29 (pl. 3, fig. 9, 1881), which has a similar angulated shaft and just a trace of the bases of the setæ. _Pygidial Appendages._ That appendages were present under the pygidium is shown by longitudinal sections, but nothing is known of the detail of structure. [Illustration: Fig. 16. Restoration of _Calymene senaria_ Conrad, based upon data obtained from the study of the translucent sections made by Doctor Walcott. Prepared by Doctor Elvira Wood, under the supervision of the author. About twice natural size.] _Relation of Hypostoma to Cephalon in Calymene._