. Bulletin - United States National Museum. Science. ^m. Fig. 190.—Dittopora colliculata. a, small portion of a tangential section, X20, with the walls OF THE MESOPOEES VISIBLE. THE LARGE AND SMALL SET OF ACANTHOPORES ARE CLEARLY DEVELOPED; 6, ANOTHER TANGENTIAL SECTION, X20, WITH THE MESOPORES AND SMALL ACANTHOPORES OBLITERATED BY THE INTERZOCECIAL TISSUE. THIS THIN SECTION WAS PREPARED FROM A SPECIMEN IDENTIFIED BY DYBOWSEI AS TREMATOPORA PXJSTULIFERA; C, VERTICAL SECTION, X20, SHOWING THE OCCURRENCE OF SEMIDIAPHRAGMS ONLY IN THE BEND TO THE MATURE ZONE. WASSALEM BEDS (D3), UXNOEM AND Wassal
. Bulletin - United States National Museum. Science. ^m. Fig. 190.—Dittopora colliculata. a, small portion of a tangential section, X20, with the walls OF THE MESOPOEES VISIBLE. THE LARGE AND SMALL SET OF ACANTHOPORES ARE CLEARLY DEVELOPED; 6, ANOTHER TANGENTIAL SECTION, X20, WITH THE MESOPORES AND SMALL ACANTHOPORES OBLITERATED BY THE INTERZOCECIAL TISSUE. THIS THIN SECTION WAS PREPARED FROM A SPECIMEN IDENTIFIED BY DYBOWSEI AS TREMATOPORA PXJSTULIFERA; C, VERTICAL SECTION, X20, SHOWING THE OCCURRENCE OF SEMIDIAPHRAGMS ONLY IN THE BEND TO THE MATURE ZONE. WASSALEM BEDS (D3), UXNOEM AND Wassalem, Esthonia. Mesopores closed at the surface, and so numerous as to isolate the zooecia. The important features shown in tangential sections are the oval, frequently constricted zooecia with thick, ring-like walls, the large acanthopores with well defined central space, and the smaller, more granular acanthopores irregularly placed in the inter-zooecial spaces. Such sections prepared from near the surface of well developed speci- mens show only a dense tissue penetrated by the smaller acanthopores in the interzooecial spaces (fig. 190 &), but in deeper sections (fig. 190 a), the outhnes of the mesopores are visible. On account of the thickness of the mature zone, it is difficult to prepare vertical sections showing the full length of the zooecial tubes. This difficulty was experienced by Dybowski, as is evidenced by his figured vertical section (pi. 3, fig. 4b) of the type form of the spe-. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original United States National Museum; Smithsonian Institution; United States. Dept. of the Interior. Washington : Smithsonian Institution Press, [etc. ]; for sale by the Supt. of Docs. , U. S. Govt Print. Off.
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