124 
Acanthostyles are common and have an average diameter of 0.03 
mm and density of 29.5 per mm?*. They originate deep in the 
exozone, extend the length of the exozone, and are composed of a 
hyaline calcite core surrounded by steeply dipping conical laminae. 
Autozooecial wall thickness averages 0.08 mm in the exozone. 
Wall microstructure is composed of steeply inclined, V-shaped 
laminae. The zooecial boundaries are, however, indistinct. Zooecia 
are frequently infilled with laminar calcite close to the zoarial 
surface. In longitudinal section this infilling consists of broad U- 
shaped laminae. 
REMARKS. Leioclema sp. B is primarily characterised by: the 
small size of the erect branches; autozooecial apertures rounded in 
transverse section throughout the colony; an exozone which is very 
wide in comparison with the endozone; common rounded 
mesozooecia containing abundant diaphragms; and small but long 
acanthostyles. Only one specimen is known from Clog-y-fran. 
Leioclema sp. B can be distinguished from Leioclema sp. A by the 
smaller colony size. 
Owen (1962, 1965, 1969) described numerous species of 
Leioclema and the related Asperopora from the Silurian of the Welsh 
Borderland and Shropshire. L. halloporoides Owen, 1962 was de- 
scribed from the Ludlow Aymestry Limestone of Shropshire. This 
also has very small colony branches (2 mm diameter) and 
mesozooecia containing diaphragms. Leioclema sp. B, however, has 
more abundant diaphragms within the mesozooecia and larger 
acanthostyles 
Leioclema sp. B is possibly a new species but, as it is represented 
only by one poorly preserved specimen, no specific name will be 
assigned until further material is obtained. 
Leioclema? sp. Figs 12-13 
MATERIAL. NHM PD 8316-8318. 
DESCRIPTION. Zoaria erect with thick cylindrical branches, on 
average 12 mm in diameter. 
Autozooecia curve outwards gradually from the branch axis to 
meet the zoarial surface at 90°. The autozooecia within the endozone 
have very thick walls. 
The exozone has an average diameter of 2.28 mm. It is recognised 
by a slight thickening of the zooecial walls. Autozooecia all origi- 
nate in the endozone where they are rounded-polygonal in transverse 
section; they become irregular-rounded in the exozone, as seen in 
tangential sections of branches. Autozooecial diameters average 
0.37 mm x 0.45 mm within the exozone. Thin basal diaphragms, 
which are orally-deflected at their junctions with the zooecial walls, 
are rare. 
Mesozooecia occur in the exozone, on shallow tangential sec- 
tions. They are rounded with a maximum diameter averaging 0.14 
mm, and contain abundant, thick, orally-deflected, basal diaphragms, 
which are spaced on average 0.13 mm apart in the endozone and 0.1 
mm in the exozone. 
Acanthostyles are large and abundant with an average diameter of 
0.09 mm and density of 12.5 per mm’. They vary greatly in size, 
ranging in diameter from 0.05 mm to 0.12 mm, and originate 
throughout the colony. They are often wider than the zooecial walls. 
The acanthostyles are composed of a broad hyaline core; no sheath- 
ing laminae can be identified. 
Autozooecial wall thickness averages 0.06 mm in the exozone. 
Wall microstructure is composed of inclined, V-shaped laminae, but 
is exceedingly poorly preserved. 
REMARKS. Only three fragmentary specimens of this species have 
C. BUTTLER 
been found. The colonies are erect with thick autozooecial walls. 
The autozooecia are rounded-polygonal to slightly petaloid in shal- 
low tangential section. Rounded mesozooecia are present and have 
abundant diaphragms. Diaphragms are rare in autozooecia. 
Acanthostyles are large and abundant throughout the colony, occa- 
sionally inflecting autozooecial walls. 
Identification of the species is difficult because of the poor 
preservation of the material. The abundance of diaphragms in the 
mesozooecia and the lack of them in the autozooecia fit within the 
generic concept of Leioclema followed here. However, the 
acanthostyles are large (often wider than the zooecial walls), abun- 
dant and originate throughout the colony. A thick hyaline core is 
identifiable but no surrounding laminae are present, as found in the 
acanthostyles of other species of Leioclema. The acanthostyles are 
similar to those observed in the early Ordovician genus Orbipora 
Eichwald, 1856, illustrated in Astrova (1978: pl. 11, fig.i) and Taylor 
& Cope (1987: fig.1). Orbipora is, however, characterised by its 
massive form and absence of mesozooecia. 
The precise taxonomic placing of the species is uncertain because 
of the poor quality of the material available. The specimens are 
therefore tentatively designated Leioclema? sp. 
Family HALLOPOROIDAE Bassler, 1911 
Genus HALLOPORA Bassler, 1911 
Hallopora peculiaris Pushkin, 1987 Fig. 14 
1987  Hallopora wesenbergiana peculiaris Pushkin in Ropot & 
Pushkin: 153; pl. 8, fig. 5, pl. 9, fig. 1. 
1991b Hallopora peculiaris Pushkin; Buttler: 86; pl. 3, figs 3-8. 
MATERIAL. NHM PD 8396. 
OTHER OCCURRENCES. Piriguskii Stage (Lower Ashgill, upper 
Ordovician), Shikipi, Latvia (see Pushkin in Ropot & Pushkin, 
1987), Slade and Redhill Beds (upper Rawtheyan, Ashgill), A40 
Pengawse Hill diversion, W. of Whitland, Dyfed, Wales (SN 164170) 
(see Buttler 1991b). 
DESCRIPTION. Zoarium erect with cylindrical branches on average 
5.7 mm in diameter. 
Autozooecia curve gradually away from the branch axis in the 
endozone and meet the zoarial surface at approximately 80—90°. In 
the endozone the zooecial walls are very thin. 
The exozone, recognised by a thickening of the zooecial walls, 
has an average width of 1.52 mm. Autozooecia are circular in 
transverse section throughout the colony and average 0.29 mm in 
diameter in the exozone. Diaphragms are rare within the autozooecia 
and when present, usually occur closely spaced in the distal exozone. 
These basal diaphragms are orally-deflected at their junctions with 
the zooecial walls and their laminae are generally continuous with 
the zooecial linings. The average spacing between diaphragms is 
0.17 mm in the exozone. 
Mesozooecia are common throughout the whole zoarium, often 
originating in the inner parts of the endozone. Mesozooecial walls 
are thin in the endozone and thicken in the exozone. They are 
polygonal to polygonal-rounded in shallow tangential sections. 
Basal diaphragms are present throughout their length, spaced on 
average 0.1 mm apart in the endozone and 0.07 mm in the exozone. 
Diaphragms tend to increase in thickness distally along the 
mesozooecia. In some colonies mesozooecial walls are constricted 
at the position of the diaphragms, producing a slightly beaded 
appearance. 
