. Bulletin of the Natural Histort Museum. Geology series. 128 C. BUTTLER. Fig. 20 Eridotrypa simulatrix (Ulrich, 1890), NHM PD 8343; 20a, longitudinal section, x25; 20b, transverse section, x25; 20c, tangential section, x53; 20d, tangential section, xl03. Fig. 21 Monticulipora aff. compacta Coryell. 1921, NHM PD 8328; 21a, longitudinal section, x30; 21b, transverse section, x22; 21c, tangential section, x86. Fig. 22 Homotrypa cf. similis Foord 1883, NHM PD 8323; 22a, longitudinal section, x30; 22b, transverse section, x30. Acanthostyles are abundant with an average diameter of mm and dens
. Bulletin of the Natural Histort Museum. Geology series. 128 C. BUTTLER. Fig. 20 Eridotrypa simulatrix (Ulrich, 1890), NHM PD 8343; 20a, longitudinal section, x25; 20b, transverse section, x25; 20c, tangential section, x53; 20d, tangential section, xl03. Fig. 21 Monticulipora aff. compacta Coryell. 1921, NHM PD 8328; 21a, longitudinal section, x30; 21b, transverse section, x22; 21c, tangential section, x86. Fig. 22 Homotrypa cf. similis Foord 1883, NHM PD 8323; 22a, longitudinal section, x30; 22b, transverse section, x30. Acanthostyles are abundant with an average diameter of mm and density of 47 per min-. They originate throughout the whole colony and occasionally indent autozooecial apertures. The acanthostyles are composed of a hyaline calcite core surrounded by steeply dipping conical laminae. Autozooecial wall thickness averages mm in the exozone. Wall microstructure is composed of steeply inclined, V-shaped laminae. It is, however, indistinct due to the presence of the acanthostyles. Occasional zooecia are infilled with laminar calcite close to the zoarial surface. In longitudinal section this infilling consists of broad U-shaped laminae. Remarks. This species is characterised by the ramose colony form and autozooecial apertures which are rounded in shallow tangential section. Zooecial walls are thin in the endozone. thicken- ing in the exozone. Diaphragms and/or cystiphragms occur in the autozooecia, while the mesozooecia contain only diaphragms. Acanthostyles are abundant throughout the colony. This is the only species of Monticulipora encountered in the present study and the material is poorly preserved and visible only in section. Monticulipora compacta Coryell, 1921, described from the Pierce Limestone(Caradoc), Tennessee, USA (Coryell 1921: 283),Novaya Zemlya, Vaigach, and Stodolbskgo (middle Ordovician), Zapadno- Arkticheska Province. Russia (Astrova 1965: 197). has a pattern of diaphragms and cystiphragms, and rare mesozooecia similar to the
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