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Show APPENDIX B.- PALEONTOLOGY. 418 ALLOBISMA TEBMINALIS, Hall, ( n. sp.) PLATE IY. FIG. 4 a b. Shell elongate- ovoid, with the posterior extremity extended and sub- acute; beaks anterior, or in a line with the anterior extremity of the shell; surface marked by strong concentric ridges, which, diverging from the beak, are more prominent on the central portion of the shell, and gradually die out on the cardinal line. The shell is also tjuite smooth toward the basal margin, with the exception of the rather coarse concentric striae which cover the entire surface* Fig. 4 a, view of the left valve. Fig. 4 b, anterior view of the shell. Loc. from the Big Blue River. NUCULA ARATA, Hall, ( n. sp.) PLATI IV. FIG. 5 a b. Shell oval- ovate, rounded before, and gradually narrowing behind the beaks ( posterior extremity broken off); beaks prominent, closely incurved; posterior lunule elongated and distinctly defined; surface marked by distinct ( rather sharp where unworn) equal concentric ridges, scarcely so wide as the furrows between them. The ridges, when seen in a longitudinal direction, have an imbricated appearance. Fig. 5 a, the right valve, showing the anterior extremity broken off. Fig. 5 b, a cardinal view, showing the beaks and defined posterior lunule. This beautiful species occurs with Terebratula, Spinfer, and ProduetuSj in a decomposing limestone, on the east side of the Missouri Eiver, below Weston. GASTEROPODA. PLEUBOTOMABIA CORONULA, Hall, ( n. sp.) PLATI IV. Fio. 6 a b o d. ' ' K Depressed trochiform, volutions about five, angular, slightly convex on the upper side, and sloping almost uniformly from4he suture to the margin; lower surface more rounded; aperture sub-quadrangular; striae bent abruptly backward on the acute outer |