. Bulletin - United States National Museum. Science. 98 BULLETIN 11, UNITED STATES NATIONAL MUSEUM. excrescences. Zocecia large, with moderately thin walls, dnect, hexagonal or sub- rhomboidal apertures. The latter are subequal (there being no distinguishable clusters of large ones), are arranged in rather regular series with 11 in 5 mm. Lunarium well developed, appearing as a small crescentic elevation usually in one of the angles. Mesopores few, sometimes appearing to be absent entirely, occasionally forming small clusters of from two to six. Internal characters.—In tangential sections the w
. Bulletin - United States National Museum. Science. 98 BULLETIN 11, UNITED STATES NATIONAL MUSEUM. excrescences. Zocecia large, with moderately thin walls, dnect, hexagonal or sub- rhomboidal apertures. The latter are subequal (there being no distinguishable clusters of large ones), are arranged in rather regular series with 11 in 5 mm. Lunarium well developed, appearing as a small crescentic elevation usually in one of the angles. Mesopores few, sometimes appearing to be absent entirely, occasionally forming small clusters of from two to six. Internal characters.—In tangential sections the walls of contiguous zocecia appear to be thoroughly amalgamated, the lunarium is represented by two or three small lucid spots (lunarial tubuli) on one side of the tube, the end ones projecting slightly into its cavity. In vertical sections the tubes are scarcely to be called vertical even in the axial region, ciu-v- c ing outward with a uni- form curve from the be- ginning. Their walls are composed of rapidly alter- nating dark and lighter shades of schlerenchyma, so that they appear more or less distinctly lineate transversely. The cause of these lines, which are closest in the peripheral part of the zoarium, is unknown, unless the light ones, which are of uni- form width and, espe- cially in the axial region, narrower than the dark bands, represent rows of perforations. Exceed- ingly delicate dia- phragms, their diameter or more apart, occur chiefly in the outer and middle part of the tubes. The axial portion of transverse sections is very nearly like tangential, the only difference being that the walls are a little thinner and small tubes comparatively more abundant. Occurrence.—^Very abundant in the Stictoporella bed of the Black River (Decorah) shale at various localities in Minnesota and Iowa. Rather uncommon in the Kuckers shale (C2), Baron Toll's estate, near Jewe, Esthonia. ' Plesiotype.—Cat. No. 57204, One specimen from Baron Toll's estate is in the col
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