. Bulletin - United States National Museum. Science. 294 BULLETIN 77, UNITED STATES NATIONAL MUSEUM. The massive zoarium, extremely thin-walled polygonal zooecia, absence of acanthopores, few mesopores, crenulated zocecial tube and numerous semidiaphragms of H. subspliericum should suffice to dis- tinguish it from associated as well as other massive bryozoans. Externally Monotrypa jewensis is quite similar, but the vertical frac- ture of H. subspliericum showing semidiaphragms will distinguish them. A globose EemipJiragma in the lowest Trenton strata of the United States is closely related to
. Bulletin - United States National Museum. Science. 294 BULLETIN 77, UNITED STATES NATIONAL MUSEUM. The massive zoarium, extremely thin-walled polygonal zooecia, absence of acanthopores, few mesopores, crenulated zocecial tube and numerous semidiaphragms of H. subspliericum should suffice to dis- tinguish it from associated as well as other massive bryozoans. Externally Monotrypa jewensis is quite similar, but the vertical frac- ture of H. subspliericum showing semidiaphragms will distinguish them. A globose EemipJiragma in the lowest Trenton strata of the United States is closely related to the form under discussion, but as it remains undescribed, comparisons are unnecessary. Occurrence.—^Abundant in the Wesenberg limestone (E) at Wesen- berg, Esthonia, and vicinity. Cotypes.—Cat. No. 57423, Specimens and thin sections in the collection of the British Museum. HEMIPHRAGMA ROTUNDATUM, new species. Text fig. 180. The type-specimen of this species is a rounded, subpyriform mass, about 20 mm. long and 14 mm. in diameter, with a smooth, cellulif- erous surface and inconspicuous maculae. The zooecial apertures are direct, angular, thin-walled, and exhibit sharp acanthopores of medium size at many of their junction angles. Five to six occur in 2 mm. The mesopores are angular, usually small and few, seldom. Fig. 180.—Hemipheagma rottjndatum. a, side view of the type-specimen, natural size; 6, tan- gential SECTION OF THE TYPE, X20; C, A VERTICAL SECTION, X20, ILLUSTRATING THE TABULATION OF BOTH ZOCECIA AND MESOPORES; d, A FEW ZOCECIA, X35. ORTHOCERAS LIMESTONE (B3), ISLAND OF RoGo, Esthonia. numerous enough to isolate the zooecia. Under a hand lens maculae composed of larger zooecia and more numerous mesopores may be observed at regular intervals. The zooecial apertures, when likewise magnified, often exhibit the semidiaphragms at or near the surface as a partition extending half way across the opening. Vertical sections exhibit two features in particular. Fi
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