This species is represented by a single tooth from the cretaceous sandstone near the Garden of the Gods, Col. It does not agree exactly with any descriptions or plates which we have seen; but the differences are probably owing to the position or age of the specimen. The crown is low, broad, and not very acute, the edge is finely serrate, and there is no sensible difference between the serrations of the two borders. The anterior border is undulating in outline, but for the most part is convex; the posterior is short and straight, and sends out quite a long heel. One face of the crown is flat and the other is strongly convex. The root is stout and divided into two fangs, which are longer and more distinct than is common in this species. There are no denticles; cementum smooth. _Measurements._ M. Length of crown ·017 Depth of fang ·009 Height of crown ·011 Galeocerdo hartwellii, Cope. Cret. Vert, p.. 244. This species belongs to the group _G. Egertonii_, Ag., having the two edges subequal and symmetrical. A single tooth from Cement Gulch, Col. _CESTRACIONTIDÆ._ "Two dorsal fins, an anal; nasal and buccal cavities confluent. Teeth obtuse, several series being in function." (Günther.) Ptychodus, Ag. Poissons Fossiles, t. iii., p. 56. Ptychodus Whippleyi, Marcou. Geology of North America, 1858, p. 33. Represented by a tooth from the cretaceous of Cement Gulch, almost identical with the specimen described by Dr. Leidy from the cretaceous of Texas. (Cont. to Ext. Vert. Fauna, p. 300.) SUMMARY. MAMMALIA. Primates 4 Carnivora 2 Perissodactyla 16 Artiodactyla (?) 1 Amblypoda 3 Rodentia 1 -- 27 AVES. Incertæ sedis 4 -- 4 REPTILIA. Crocodilia 6 Chelonia 5 -- 11 PISCES. Teleocephali 3 Nematognathi 1 Cycloganoidei 6 Plagiostomata 3 Incertæ sedis 1 -- 14 -- Total 56 EXPLANATION OF PLATE A. _Figure about one fourth natural size._ Uintatherium Leidianum. [Illustration] EXPLANATION OF PLATE I. _Figure three fourths natural size._ Palæosyops paludosus. Posterior view of cranium. [Illustration] EXPLANATION OF PLATE II. _Figures one fourth natural size._ Palæosyops major. Fig. 1.--Axis, view of right side. Fig. 2.--Axis, anterior view. Fig. 3.--Atlas, posterior view. Fig. 4.--Atlas, anterior view. Figs. 5 and 6.--Seventh cervical anterior and posterior view. Figs. 7 and 8.--Anterior and posterior views of right tibia.