ORDOVICIAN BRYOZOA FROM THE LLANDEILO LIMESTONE 
Autozooecia curve outwards gradually from the branch axis to 
meet the zoarial surface at 90°. Autozooecia within the endozone 
have thin, slightly wavy walls. 
The exozone is narrow with an average width of 0.57 mm. It is 
recognised by a thickening of the zooecial walls. Autozooecia all 
originate in the endozone where they are rounded-polygonal in 
transverse section, becoming rounded to slightly petaloid in the 
exozone as seen in tangential sections of branches. Autozooecial 
diameters average 0.19 mm in the exozone. Diaphragms are rare in 
the autozooecia, and when present only one or two are found in the 
outer endozone and exozone. These basal diaphragms are all orally- 
deflected at their junctions with the zooecial walls. 
Mesozooecia are common and originate throughout the endozone; 
their shape in shallow tangential section has not been observed. 
Orally deflected basal diaphragms are found along the entire length 
of the mesozooecia. Vertical walls are extensively constricted at the 
positions of the diaphragms, producing a pronounced beaded (in 
some cases vesicular) appearance. 
Acanthostyles are large and abundant, with an average diameter 
of 0.05 mm. They originate throughout the colony and commonly 
indent the autozooecia. Acanthostyle microstructure is difficult to 
distinguish, but seems to consist of a hyaline core surrounded by 
steeply dipping conical laminae. 
Autozooecial wall thickness averages 0.06 mm. Wall microstruc- 
ture is composed of inclined laminae, but is hard to distinguish 
because the walls are greatly disrupted by acanthostyles. Frequently, 
the zooecia are infilled with laminar calcite close to the zoarial 
surface. The zooecia in large parts of the colony have been found to 
be all infilled. In shallow tangential sections of these areas, all that is 
seen is the laminar calcite wall pierced by acanthostyles. 
REMARKS. Only one poorly preserved specimen of this species 
has been found. It is characterised by the ramose colony form and 
meandering endozonal walls. Autozooecia are rounded to slightly 
petaloid in shallow tangential sections, and beaded mesozooecia are 
common throughout the colony. Diaphragms are rare in autozooecia 
but abundant in mesozooecia throughout the colony. The irregularly 
shaped, beaded zooecia make this a particularly characteristic spe- 
cies and distinguish it from H. sladei described by Buttler (1991b). 
Identification is, however, left in open nomenclature until better 
preserved material can be examined. 
Heterotrypa sp. is similar to the Russian species H. ovata Astrova, 
1957, but has more weakly beaded zooecia and less prominent 
acanthostyles. 
Genus LEIOCLEMA Ulrich, 1882 
Leioclema sp. A Figs 8-10 
MATERIAL. NHM PD 8307-8308. 
DESCRIPTION. Zoaria erect with cylindrical branches on average 8 
mm in diameter. 
Autozooecia curve outwards gradually from the branch axis to 
meet the zoarial surface at 80°-90° and have moderately thick, 
slightly wavy walls within the endozone. 
The exozone is quite large with an average diameter of 1.9 mm. It 
is recognised by an extensive thickening of the zooecial walls. 
Autozooecia all originate in the endozone, where they are rounded- 
petaloid in transverse section becoming extensively petaloid in the 
exozone as seen in tangential sections of branches. Autozooecial 
diameter averages 0.18 mm by 0.26 mm within the exozone. Dia- 
phragms are rare and frequently wholly absent in autozooecia. 
123 
Mesozooecia are very common and originate in the outer parts of 
the endozone and inner parts of the exozone. They are rounded and 
have a maximum diameter averaging 0.09 mm. The mesozooecia 
contain abundant orally-deflected basal diaphragms, spaced on 
average 0.15 mm apart in the endozone and 0.1! mm apart in the 
exozone, with successive diaphragms often increasing in thickness 
distally along the mesozooecia. 
Acanthostyles are large and very abundant with an average diam- 
eter of 0.03 mm and density of 29.5 per mm?. They originate 
throughout the colony and are very abundant in the exozone, where 
they indent the autozooecial apertures, producing a petaloid shape. 
Acanthostyles are larger in size in the outer exozone than in the rest 
of the colony. In longitudinal section acanthostyles can be identified 
protruding into the zooecial chambers. Acanthostyles are composed 
of a broad hyaline core surrounded by steeply dipping conical 
laminae. 
Autozooecial wall thickness averages 0.13 mm in the exozone. 
Wall microstructure is composed of steeply inclined, U-shaped 
laminae. In tangential sections a thick granular layer can be identi- 
fied between adjacent zooecia. Virtually all mesozooecia, and some 
autozooecia, are infilled with laminar calcite close to the zoarial 
surface. In longitudinal section this infilling consists of broad U- 
shaped laminae. The infilling of the mesozooecia commences in the 
middle exozone, whereas the autozooecia are infilled in the outer 
exozone. 
REMARKS. Only two poorly preserved specimens of this species 
have been found at Clog-y-fran. The colonies are primarily recog- 
nised by the erect form, and by autozooecial walls that are thick 
throughout the colony. Autozooecial apertures are rounded-petaloid 
in transverse section and markedly petaloid in shallow tangential 
section. Rounded mesozooecia are common with abundant dia- 
phragms; diaphragms are rare in the autozooecia. Acanthostyles are 
present throughout the colony; they are large and abundant in the 
exozone. 
The identification of this species is difficult because of the poor 
quality of the two known specimens. Leioclema sp. A is placed in 
open nomenclature until better preserved material can be obtained 
and a complete description of this possibly new species can be made. 
Leioclema sp. B Fig. 11 
MATERIAL. NHM PD 8306. 
DESCRIPTION. Zoaria erect with very thin cylindrical branches, on 
average 1.5 mm in diameter. 
Autozooecia curve away gradually from the branch axis in the 
endozone and then more abruptly in the exozone to meet the zoarial 
surface at 90°. Autozooecia within the endozone all have straight 
thin walls. 
The exozone is extremely broad with an average width of 0.67 
mm. It is recognised by a simultaneous thickening of zooecial walls 
and a change in zooecial orientation. Autozooecia all originate in the 
endozone where they are rounded in transverse section. They retain 
this shape in the exozone, as seen in tangential sections of branches. 
Autozooecial diameters average 0.09 mm by 0.11 mm within the 
exozone. Diaphragms are absent in the autozooecia. Occasional 
cystiphragms can, however, be found in the outer exozone. 
Mesozooecia are common and originate in the inner parts of the 
exozone. They are rounded in shape in tangential sections and have 
a maximum diameter averaging 0.04 mm. The mesozooecia contain 
abundant orally deflected, thick, basal diaphragms, spaced on aver- 
age 0.04 mm apart, and generally increasing in thickness distally 
along the mesozooecia. 
