Shell thick, moderately large, subequivalvular, rather convex, quite oblique, ears well developed. The hinge is nearly straight, the beak does not project, the angle of divergence of its sides is about eighty to ninety degrees. The left valve, exclusive of the ears, is ovate; anterior ear well developed, obtusely angular, marked only by strong lines of growth; the rise from the ear to the body of the shell is abrupt; the marginal sinus separating the ear from the rest of the shell broad, shallow, and ill-defined. The posterior ear is unknown. The anterior margin below the ear forms an ovate curve, which is probably continued on the ventral and postero-ventral margins. The surface of this valve is apparently marked only by stronger and fainter concentric lines except on the front and back sides, where there are radiating rows of vaulted lamellæ. It is entirely probable that these marks once extended over the entire surface, but have been worn off from the more convex portions. Judging from another specimen, the right valve is somewhat flatter than the left and quite as oblique. Posterior ear very small and obtuse; anterior ear quite large, marked by obscure, large, radiating ribs and probably vaulted lamellæ, as well as strong concentric markings; separated from the shell by a deep sulcus. Margin from the beak around the posterior to near the middle of the shell is a regular ovate curve, antero-ventral margin somewhat produced but rounded, extending obliquely toward the beak until the deep byssal sinus is reached. Ornamentation as in the other valve. In this specimen it seems that the radiating rows of scales covered the entire surface before being worn away. Length, 36 mm.; height, 32 mm.; hinge, 17 mm.; thickness, about 5 mm. Position and locality: Thin limestone, south of Dover, Kan., in Upper Coal Measures. Type in author’s collection. This shell may prove to be a _Pseudomonotis_, as the critical characters are not well known. It is not liable to be confused with any other shell from the Coal Measures. =Pinna lata=, n. sp. Plate V, fig. 4. Shell small for this genus, not very convex, probably plain except the usual growth marks, acutely pointed at the beaks, which are terminal. The angle of divergence of the shell is thirty degrees. This species is based on three casts. The type is not distorted, but the posterior end is broken away. There are two other specimens from the same locality, but compressed dorso-ventrically, which show the same characters as the type. The size is about that of _Aviculopinna americana_ Meek, but the form and markings as shown on the cast are very different, and the beaks are terminal. Length of type along hinge, 27 mm.; height (20 mm. back of beak), 11 mm. Position and locality: Carboniferous, Upper Coal Measures, Howard limestone, Topeka, Kan.