ORDOVICIAN BRYOZOA FROM THE LLANDEILO LIMESTONE 
Autozooecial wall thickness averages 0.1mm in the exozone. 
Wall microstructure is composed of steeply inclined, V-shaped 
laminae. The precise contact between the zooecia is indistinct. The 
thickened exozonal diaphragms in the mesozooecia are also laminar 
and are continuous with the wall laminae. 
Maculae composed of a concentration of mesozooecia can be 
recognised in thin sections. 
REMARKS. Hallopora peculiaris is primarily characterised by the 
extensive beaded mesozooecia which originate in the inner endozone. 
The autozooecia are circular throughout the colony, and diaphragms 
are rare in the endozone, becoming more abundant in the outermost 
regions. 
H. peculiaris has also been described from the Slade and Redhill 
Beds (Ashgill) of South Wales (Buttler, 1991b). 
Hallopora aff. wesenbergiana (Dybowski, 1877). Fig. 15 
MATERIAL. NHM PD 8310-8313. 
DESCRIPTION. Zoaria erect with thick cylindrical branches, on 
average 11 mm in diameter. 
Autozooecia are parallel to the branch axis in the inner endozone 
and then curve outwards gradually to meet the zoarial surface at 
80°-90°. Within the endozone autozooecial walls are thin and 
straight. 
The exozone is difficult to distinguish; it can be recognised by a 
slight thickening of the zooecial walls. Autozooecia all originate in 
the endozone where they are polygonal-rounded in transverse sec- 
tion, becoming circular in the exozone as seen in tangential sections 
of branches. Autozooecial diameters average 0.21 mm by 0.27 mm 
within the exozone. Diaphragms are very abundant throughout the 
autozooecia. In the endozone there are periodic concentrations of 
diaphragms which occur throughout the colony at the same level. 
Within the concentrations, diaphragms are spaced on average 0.1 
mm apart; elsewhere they are spaced on average 0.6 mm apart. In the 
exozone, diaphragms are very abundant and on average spaced 0.11 
mm apart. All the diaphragms are basal and orally-deflected at their 
junctions with the zooecial walls. 
Mesozooecia are present, originating in the outer parts of the 
endozone and inner parts of the exozone. They are rounded in 
shallow tangential sections and have a maximum diameter averag- 
ing 0.1 mm. They contain abundant orally deflected basal diaphragms 
spaced on average 0.07 mm apart in the exozone. 
Autozooecial wall thickness averages 0.03 mm in the exozone. 
The wall microstructure is poorly preserved but vague laminations 
can be recognised in one tangential section. 
REMARKS. Hallopora aff. wesenbergiana (Dybowski, 1877) is 
characterised by the ramose colony form with thick branches. Thin- 
walled zooecia have rounded apertures in shallow tangential sections. 
Diaphragms are abundant throughout the whole colony and are 
periodically concentrated in bands, which possibly indicate periods 
of slow growth. Bassler (1911) illustrated H. wesenbergiana from 
the Wesenberg Limestone and Wassalen Beds (Caradoc) in Estonia. 
This material is similar to the Welsh; it has thin-walled autozooecia 
with abundant diaphragms, although these do not occur in bands. 
The banding, or lack of it, may not be a specific feature but may 
relate to an environmental influence acting on the colonies. The poor 
quality of the Welsh material does not allow a more precise specific 
identification. 
125 
Genus BATOSTOMA Ulrich, 1882 
Batostoma clogyfranense sp. nov. Figs 16-18 
HOLOTYPE. NHM PD 8362. 
PARATYPES. NHM PD 8353-8361, 8363-8375. 
NAME. After the type locality. 
DIAGNOSIS. Colony small, ramose. Autozooecia curve out gradu- 
ally from branch axis to zoarial surface. Autozooecial walls thin in 
endozone. Autozooecia polygonal-rounded in transverse section, 
circular in shallow tangential sections. Small polygonal-rounded 
mesozooecia present, originating in outer endozone. Diaphragms 
present in all zooecia. Acanthostyles small, abundant in exozone. 
DESCRIPTION. Zoaria erect with narrow cylindrical branches, on 
average 3.9 mm in diameter. 
Autozooecia curve out gradually from the branch axis to meet the 
zoarial surface at an angle of 70°-80°. The autozooecia within the 
endozone have thin walls. 
The exozone is narrow with an average diameter of 0.8 mm; it is 
characterised by a thickening of the zooecial walls. Autozooecia 
originate in the endozone where they are polygonal-rounded in 
transverse section, becoming circular in the exozone as seen in 
tangential sections of branches. Autozooecial diameters average 
0.15 mm by 0.18 mm in the exozone. Diaphragms are found 
throughout the autozooecia, although they are less common in the 
inner exozone. They are spaced on average 0.28 mm apart in the 
endozone, and 0.15 mm apart in the exozone. These basal dia- 
phragms are all orally-deflected at their junctions with the zooecial 
walls and their laminae are continuous with the zooecial linings. 
Mesozooecia are present and originate in the outer parts of the 
endozone. They are polygonal-rounded in shallow tangential sec- 
tions with a maximum diameter which averages 0.09 mm. 
Orally-deflected basal diaphragms are found along the length of the 
mesozooecia, spaced on average 0.07 mm apart. 
Acanthostyles are small, often irregularly shaped and highly 
abundant, with an average diameter of 0.03 mm and density of 67 per 
mm7?. They originate in the exozone and usually form a ring around 
the autozooecia, consisting of approximately ten acanthostyles. The 
acanthostyles are composed of a circular, or sometimes irregular 
hyaline core surrounded by indistinct dipping conical laminae. 
Autozooecial wall thickness averages 0.08 mm in the exozone. 
Wall microstructure is composed of inclined, U-shaped laminae; 
however, it is poorly preserved. Frequently, zooecia are infilled with 
laminar calcite close to the colony surface; in longitudinal section 
this infilling consists of broad U-shaped laminae; large sections of 
zoaria often have all the zooecia infilled in this way. 
REMARKS. Batostoma clogyfranense sp. nov. is primarily charac- 
terised by thin, straight zooecial walls, a narrow exozone, and 
diaphragms regularly spaced throughout the colony. Autozooecial 
apertures are rounded in shallow tangential section, and polygonal- 
rounded mesozooecia occur. Acanthostyles are abundant and 
occasionally irregular in shape. 
Another species of Batostoma, B. cf. polare Astrova, 1965, that is 
described here can be distinguished from B. clogyfranense by the 
thicker exozonal walls and the less abundant diaphragms in the 
exozone. 
The middle Ordovician species B. subtile Astrova (1965: pl. 50, 
fig. 2, pl. 51, fig. 1), from Vaigach Island, Novaya Zemlya, Russia, 
has a similar pattern of diaphragms within the endozone to B. 
clogyfranense. Diaphragms are, however, more abundant in the 
