ORDOVICIAN BRYOZOA FROM THE LLANDEILO LIMESTONE 
and usually form a ring around the autozooecia, approximately 14 
acanthostyles surrounding one autozooecium. The acanthostyles 
have a hyaline core surrounded by steeply dipping conical laminae. 
Autozooecial wall thickness averages 0.11 mm in the exozone. 
Wall microstructure is composed of steeply inclined, V-shaped 
laminae. Zooecial boundaries are dark, crenulated and granular. 
Some zooecia are infilled with laminar calcite close to the colony 
surface. In longitudinal section this infilling consists of broad U- 
shaped laminae. 
An intrazoarial overgrowth has been recognised which 1s continu- 
ous with the underlying branch and is composed of outer endozonal/ 
inner exozonal components. 
REMARKS. Only one specimen of Batostoma cf. polare Astrova, 
1965, has been found during this study. It is characterised by the 
ramose colony form and particularly thin autozooecial walls in the 
endozone, which thicken extensively in the exozone. Autozooecial 
apertures are circular in shallow tangential sections, and rounded 
mesozooecia, which originate in the outer endozone, are present. 
Thick diaphragms are abundant in the exozone and thin diaphragms 
occur in the endozone. Acanthostyles are small and numerous in the 
exozone. 
B. polare Astrova, 1965, described from the Varnek Stage, Vaigach 
and Novaya Zemlya, Russia, is very similar to the specimen from 
Clog-y-fran. They both have thin zooecial walls in the endozone 
which thicken in the exozone, abundant basal exozonal diaphragms, 
small mesozooecia and acanthostyles. Measurements for the Soviet 
and Welsh specimens are similar. The major difference between the 
Welsh specimen and type B. polare is the presence of the dia- 
phragms within the endozone of the former. 
Genus ERIDOTRYPA Ulrich, 1893 
Eridotrypa simulatrix (Ulrich, 1890) 
1890 Batostoma simulatrix Ulrich; 432, pl. 35, fig. 1. 
1893 Monticulopora simulatrix (Ulrich); James: 194. 
1908  Eridotrypa simulatrix (Ulrich); Cummings: 828, pl. 16, fig. 
4. 
1928  Eridotrypa simulatrix (Ulrich); Bassler: 152 
1987  Eridotrypa simulatrix (Ulrich); Ropot & Pushkin: 171, pl. 
15, fig. 2. 
MATERIAL. NHM PD 8342-8352. 
Fig. 20 
OTHER OCCURRENCES. Cincinnati Group, Savanna, Illinois, USA; 
English Head and Vaureal Formations, Anticosti Island, Quebec, 
Canada; Waynesville Formation, Harmons Station, Indiana, USA; 
Pirguskii Stage (Caradoc), Yuzhnoi, Pribaltiki, Russia. 
DESCRIPTION. Zoaria erect with narrow cylindrical branches, on 
average 3.3 mm in diameter. 
Autozooecia meander roughly parallel to the branch axis within 
the endozone and then curve slightly in the exozone to meet the 
zoarial surface at 50°. Within the endozone they have thin walls. 
The exozone is narrow with an average diameter of 0.64 mm. It is 
recognised by an extensive thickening of the zooecial walls. 
Autozooecia all originate in the endozone and are rounded-polygo- 
nal in transverse section, becoming oval-rounded in the exozone as 
seen in tangential sections of branches. In branch transverse section 
the autozooecia are larger in diameter in the inner endozone than in 
the outer endozone. Autozooecial diameters average 0.13 mm by 
0.18 mm within the exozone. Diaphragms are occasionally present 
in the endozone and exozone, spaced on average 0.35 mm apart in 
127 
the endozone and 0.13 mm in the exozone. In some specimens they 
are very abundant (PD 8348). These basal diaphragms are all 
deflected orally at their junctions with zooecial walls and their 
laminae are continuous with the zooecial linings. 
Mesozooecia are present and originate in the endozone. They are 
rounded in shallow tangential section, with a maximum diameter 
averaging 0.09 mm. Abundant orally deflected diaphragms are 
found along the length of the mesozooecia, spaced on average 0.07 
mm apart. 
Acanthostyles are small, occasionally irregular, abundant, with an 
average diameter of 0.02 mm. They are composed of a hyaline 
calcite core surrounded by indistinct dipping conical laminae. 
Autozooecial wall thickness averages 0.06 mm in the exozone. 
Wall microstructure is rather indistinct (only peels of these speci- 
mens are available) and is composed of steeply inclined, V-shaped 
laminae. Zooecial boundaries have not been distinguished. 
Autozooecia, and more especially mesozooecia, are frequently 
infilled with laminar calcite close to the zoarial surface. In longitu- 
dinal section this infilling consists of broad V-shaped laminae; large 
areas of the colony can be infilled. 
REMARKS. Eridotrypa simulatrix is characterised by the ramose 
colony with narrow branches. Autozooecial walls are thin and 
meandering in the endozone and thicken in the exozone. Autozooecial 
apertures are large and rounded/polygonal in transverse section, and 
small and oval in shallow tangential section. Diaphragms are present 
and abundant small acanthostyles occur in the exozone. 
It is not easy to compare the Russian and American specimens of 
E. simulatrix because those from North America are only illustrated 
by line drawings. The Welsh and Russian specimens appear to be 
identical but together may prove to represent a distinct species from 
the American specimens when direct comparisons have been made 
using the actual material. 
Genus MONTICULIPORA @ Orbigny, 1850 
Monticulipora aff. compacta Coryell, 1921. Fig. 21 
MATERIAL. NHM PD 8328, 8331c. 
DESCRIPTION. Zoaria erect with narrow cylindrical branches, on 
average 4 mm in diameter. 
Autozooecia curve out gradually from the branch axis in the 
endozone and meet the zoarial surface at 90°. The autozooecia 
within the endozone have thin, slightly wavy walls. 
The exozone is moderately broad with an average width of 1.05 
mm. It is recognised by a thickening of the zooecial walls. 
Autozooecia all originate in the endozone, where they are circular in 
transverse section. They become rounded in the exozone as seen in 
tangential sections of branches. Autozooecial diameters average 
0.16 mm by 0.13 mm within the exozone. Diaphragms are present 
throughout the autozooecia. They are spaced on average 0.15 mm 
apart in the endozone and increase to 0.07 mm apart in the exozone. 
The majority of the diaphragms are basal, deflected orally at their 
junctions with the autozooecial walls. Some diaphragms are possi- 
bly subterminal, but the poor preservation of the specimen does not 
allow this to be confirmed. Cystiphragms are numerous along the 
whole length of the autozooecia, especially in the exozone. The 
cystiphragms are normally restricted to one side of an autozooecium. 
Mesozooecia are uncommon, and originate in the outer parts of 
the endozone and inner parts of the exozone. They have an average 
maximum diameter of 0.08 mm, are rounded in shallow tangential 
section and contain abundant, orally deflected basal diaphragms. 
