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Fig. 20 Eridotrypa simulatrix (Ulrich, 1890), NHM PD 8343; 20a, longitudinal section, x25; 20b, transverse section, x25; 20c, tangential section, x53; 20d, 
tangential section, x103. 
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 0.03 mm 
and density of 47 per mm’. 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 0.05 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 
Welsh specimens. In tangential section (Coryell, 1921: pl. tv, fig. 6) 
the autozooecial apertures are polygonal-rounded. This figured 
section is, however, quite deep and so cannot be accurately com- 
pared with the shallow Welsh sections. In M. compacta acanthostyles 
are reported from within the axial region, but they are not identified 
from the exozone, in contrast to the Welsh material. The specimens 
described herein are therefore assigned to M. aff. compacta until 
better preserved material can be examined. 
Genus HOMOTRYPA Ulrich, 1882 
Homotrypa cf. similis Foord, 1883 Fig. 22 
MATERIAL. NHM PD 8323. 
DESCRIPTION. Zoarium erect with cylindrical branches, on aver- 
age 8 mm in diameter. 
