. Bulletin - United States National Museum. Science. 336 BtTLLETIN 11, UNITED STATES NATIONAL MUSEUM. Hall, Dybowski figured a vertical section (see pi. 5, fig. 1 T), wliich is undoubtedly of this form. His tangential section (figs. 1-1 e) may also be from specimens of the same species. His figures 1 / to 1 Ti, however, are undoubtedly based upon thin sections of Prasopora simulatrix Ulrich, an abundant hemispheric bryozoan in the Trenton strata of America. Dybowski erroneously identified these several species with Callopora nummiformis Hall, a small, discoid bryozoan from the Silurian rocks o
. Bulletin - United States National Museum. Science. 336 BtTLLETIN 11, UNITED STATES NATIONAL MUSEUM. Hall, Dybowski figured a vertical section (see pi. 5, fig. 1 T), wliich is undoubtedly of this form. His tangential section (figs. 1-1 e) may also be from specimens of the same species. His figures 1 / to 1 Ti, however, are undoubtedly based upon thin sections of Prasopora simulatrix Ulrich, an abundant hemispheric bryozoan in the Trenton strata of America. Dybowski erroneously identified these several species with Callopora nummiformis Hall, a small, discoid bryozoan from the Silurian rocks of New York and Indiana. The latter species, wliich belongs to Mesotrypa, a genus of the Monticuliporidse, has been figured by the present writer,^ and comparison will show the error of Dybowski's Fig. 211.—Hallopoea ? dtbowsioi. o, tangential section, X20, •with zocecu. less angulae than usual; 6, VEETICAL SECTION, X8, SHOWING CUEVED DIAPHEAGMS; C, SEVEEAL TUBES OF THE SAME, X20. WESENBEEG LIMESTONE (E), WeSENBEEG, EsTHONL*.. So far as the zoarial characters go, the description of Diplotrypa petropolitana will apply to the present form in every respect, and even the internal structure is somewhat similar. Tangential sections of the two species are almost identical. Slight differences exist, but these can not be described as permanent because of the variation in each in shape of zooecia and number of mesopores. In vertical sec- tions the widely separated diaphragms, three to ten tube diameters apart, in the zooecial tubes of HJ dyhowskii, are in marked contrast with the numerous diaphragms of the similar species. That this is a constant difference was shown by a study of over one hundred speci- mens of both species, each specimen falling into its particular place, with no intermediate forms. Continuing the comparison with Z>. petropolitana it is found that dylowsJcii does not possess the beaded walls characteristic of Diplotrypa. Moreover, as in other
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