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DescriptionEucyrtidium hexagonatum (p. 1489): Shell smooth, ovate, with six to seven internal septal rings. All joints (except the first) nearly of the same length; the sixth joint is the broadest. The seventh and eighth joints (broken off in the specimen figured) gradually decrease toward the constricted mouth, which is as broad as the septum between the third and fourth joints. Cephalis and thorax together pear-shaped, with circular pores, sharp lumbar stricture, and a stout, pyramidal horn of the same length. The five or six abdominal joints with regular, hexagonal pores, six or seven in course of the length of each joint. Dimensions. -Length of the shell (with eight joints) 0.2, length of each joint 0.025 to 0.03; greatest breadth (in the sixth joint) 0.1.