132 
and the Arnsbergian of Northamptonshire (Vine 1887) and Lanca- 
shire (Vine 1885), and the Pendleian of Yorkshire (Bancroft 1984, 
Vine 1881). 
Rhombopora hexagona sp. nov. Figs 26-31 
HoLoTyPE. BMNH PD9535, Upper part of the Glencar Lime- 
stone (Viséan, Asbian), Carrick Lough, County Fermanagh. 
PARATYPES. BMNH PD9536-9564; TCD.34045-34048, 34121, 
34154, 34170, 42591a, 42592c, 42602a; BELUM K2186, from the 
same locality and horizon as above, TCD.25687, near base of 
Michelinia Beds, Hook Head Formation (Courceyan), Locality 8 (of 
Dresser 1960), Lyraun Cove, Hook Head, County Wexford; 
TCD.25884, Michelinia Beds, Hook Head Formation (Courceyan), 
Locality 15 (of Dresser 1960), Brecaun Church, Hook Head, County 
Wexford, TCD.25885, Michelinia Beds, Hook Head Formation 
(Courceyan), Locality 40 (of Dresser 1960), Patrick’s Bay, Hook 
Head, County Wexford; TCD.25886, Linoproductus Beds, Hook 
Head Formation (Courceyan), Locality 92 (of Dresser 1960), Hook 
Head, County Wexford. 
DERIVATION OF TRIVIAL NAME. From the hexagonal pattern of 
heterostyles disposed around autozooecial apertures. 
DIAGNOSIS. Rhombopora with thin dichotomising cylindrical 
branches. Autozooecia are budded from a central linear axis in a 
spiral manner. Hemisepta are common: a robust inferior hemiseptum 
is present at the base of the vestibule while a thin superior hemiseptum 
is found on distal chamber walls high in the endozone. Diaphragms 
are absent. Autozooecial apertures are oval in shape, vary in size 
around branches, and are arranged in intersecting oblique and 
longitudinal rows around the zoarium. Small heterostyles are ar- 
ranged on ridges between autozooecial chambers in an interlocking 
hexagonal pattern. 
DESCRIPTION. Zoaria are composed of thin cylindrical 
dichotomising branches that form delicate erect dendroid colonies. 
No complete colonies were observed: the largest fragment measured 
3.38mm in length. 
Branching is infrequent and irregular with either dichotomous 
bifurcation or lateral perpendicular ramification, producing second- 
ary branches which are slightly narrower than those from which they 
were derived. All branches retain a constant width along their length. 
Autozooecia deviate from a central axis in a spiral fashion at low 
angles of 18° to 27°. Chambers are sub-linear in shape, five to six 
times long as wide, with a slightly attenuated zooecial base. Cham- 
bers bend marginally at the exozone and vestibules are orientated at 
low angles of between 25° and 40° to the zoarial surface. Chamber 
walls are thin (0.01 mm) in the endozone, with a compound structure 
of a granular centre surrounded by thin skeletal laminae. The 
exozone is very thin (0.03—0.15mm). In cross-section chambers are 
polygonal in shape. 
Autozooecial apertures are large to moderate in size, oval in 
shape, and arranged in 9 to 15 longitudinally and diagonally inter- 
secting rows around branches. The angle of this intersection varies 
from 45° to 75°. Long, narrow autozooecial apertures occur on 
reverse surfaces, while more equidimensional apertures are found 
towards and on obverse surfaces. Interapertural spacing is inversely 
proportional to apertural size (see Tables 9 and 12, and Figs 26a and 
28). Autozooecial apertures are surrounded by as many as 40 small, 
blunt, circular heterostyles (0.01mm in diameter) which arise from 
the base of, or from within the exozone. They are arranged in single, 
or occasionally several (particularly on reverse surfaces), rows along 
the crests of otherwise smooth interapertural walls, or occasionally 
Figs 26-30 Rhombopora hexagona sp. nov. Upper part of the Glencar 
Limestone (Viséan, Asbian), Carrick Lough, County Fermanagh; 26, 
BMNH PD95335 (holotype); 26a, colony form, x25; 26b, detail of 26a 
showing oval autozooecial apertures and disposition of heterostyles ina } 
hexagonal pattern on interapertural walls, x75; 27, BMNH PD9536 
(paratype), colony fragment, x40; 28, BMNH PD9537 (paratype), view 
of ‘reverse’ surface showing long, thin autozooecial apertures, x25; 29, 
BMNH PD9560 (paratype), longitudinal section showing autozocecial 
chambers with thin superior (labelled ‘s’) and thick inferior (labelled ‘i’) ” 
hemisepta, x35; 30, BMNH PD9563 (paratype); 30a, transverse section 
showing circular branch outline, zooecia budded from a central axial 
area, with thin walls in the endozone and thicker walls in the exozone, 
x35: 30b, detail of 30a showing heterostyles on interapertural walls, x75.| 
