In the same year Woodward (1884, p. 162, fig. 1-3) reproduced all of Mickleborough's figures, and suggested that the last seven pairs of appendages on the pygidium of _Calymene_ and _Isotelus_ were probably "lamelliform branchiferous appendages, as in _Limulus_ and in living Isopoda." Professor Beecher published, in 1902, an outline taken from Mickleborough's figure of this specimen, to call attention to certain discontinuous ridges along the axial cavity of the anterior part of the pygidium and posterior end of the thorax. These ridges are well shown in Mickleborough's figure, though not in that of Walcott, and their presence on the specimen was confirmed by a study by Schuchert, who contributed a diagrammatic cross-section to Beecher's paper (1902, p. 169, pl. 5, figs. 5, 6). Beecher summarized in a paragraph his interpretation of this specimen: The club-shaped bodies lying within the axis are the gnathobases attached at the sides of the axis; the curved members extending outward from the gnathobases are the endopodites; the longitudinal ridges in the ventral membrane between the inner ends of the gnathobases are the buttresses and apodemes of the mesosternites; the slender oblique rod-like bodies shown in the right pleural region in Walcott's figure are portions of the fringes of the exopodites. In 1910, Mr. W. C. King of Ottawa, Ontario, found at Britannia, a few miles west of Ottawa, the impression in sandstone of the under surface of a large specimen of _Isotelus arenicola_, described on a later page (p. 39). Finally (1918, p. 133, pl. 24, figs. 3, 3a; pl. 25), Walcott has redescribed the specimen from Ohio, presenting a new and partially restored figure. He refers also to the specimen from Ottawa under the name _Isotelus covingtonensis?_ Foerste (not Ulrich). He advances the view, which I am unable to share, that the cylindrical appearance of the segments of the appendages of _Isotelus_ is due to post-mortem changes. =Isotelus latus= Raymond. (pl. 10, fig. 1.) Illustrated: _Asaphus platycephalus_ Billings, Quart. Jour. Geol. Soc., London, vol. 26, 1870, pl. 31, figs. 1-3; pl. 32, figs. 1, 2.--Woodward, Geol. Mag., vol. 8, 1871, pl. 8, figs. 1, 1a.--Gerstäcker, in Bronn's "Klassen u. Ordnungen d. Thier-Reichs," 1879, pl. 49, fig. 1.--von Koenen, N. Jahrb. f. Min., etc., vol. 1, 1880, pl. 8, fig. 8.--Milne-Edwards, Ann. Sci. Nat., Zoologie, ser. 6, vol. 12, 1881, pl. 12, fig. 45. _Isotelus latus_ Raymond, Bull. Victoria Mem. Mus., Geol. Survey Canada, No. 1, 1913, p. 45 (species named). _Isotelus covingtonensis?_ Walcott (not Foerste), Smithson. Misc. Coll., vol. 67, 1918, p. 134. Knowledge of the appendages of this species is derived from the specimen which Billings described in 1870. It was found in the Trenton, probably the Middle Trenton, near Ottawa, Ontario, and is preserved in the Victoria Memorial Museum at Ottawa.