Bull. nat. Hist. Mus. Lond. (Geol.) 53(2): 117-134 
Issued November 1997 
Ordovician Bryozoa from the Llandeilo 
Limestone, Clog-y-fran, near Whitland, South 
Wales 
CAROLINE BUTTLER 
Department of Geology, National Museums and Galleries of Wales, Cathays Park, Cardiff, CF 1 3NP. 
Synopsis. A diverse bryozoan fauna is described from the Llandeilo Limestone (from the upper part of the classical Llandeilo 
Series), Clog-y-fran, between Whitland and St. Clears, Carmarthenshire, Wales. The fauna is dominated by trepostomes (17 
species) but one cryptostome and two fenestrate species are present. Two new trepostome species, Dittopora sanclerensis and 
Batostoma clogyfranensis, are described. 
INTRODUCTION 
Ordovician bryozoans from Britain have been neglected. This ne- 
glect can be attributed to poor preservation, the need to prepare 
oriented thin sections for identification, and also to the lack of a 
strong tradition of bryozoan research in Britain. Bryozoans are 
commonly preserved in Ordovician rocks as decalcified moulds 
which are easy to recognise but are very difficult to identify to genus 
and species level. Calcified specimens are often only noticed when 
a rock is cut and thin sections or peels are prepared. 
The bryozoan fauna from Clog-y-fran is particularly important 
because it is the most diverse of those described from the Ordovician 
of the British Isles. In the only previous study of a Welsh mid- 
Ordovician bryozoan fauna, Spjeldnaes (1963) described upper 
Llanvirn/lower Llandeilo silicified material from south Wales. This 
included abundant bryozoans: six trepostome species, two bifoliate 
cryptostomes and arthrostylid fragments. Due to the silicified pres- 
ervation identification is particularly difficult and only two species 
were named: Orbignyella favulosa? (Phillips) and Mesotrypa aft. 
lens (M’Coy). 
MATERIAL 
The Llandeilo limestone crops out in Carmarthenshire, near Clog-y- 
fran Farm (SN 239161) (Strahan et al. 1909) between Whitland and 
St. Clears and to the south of Pont-y-fenni (Fig. 1). Collection in situ 
is no longer possible but blocks from a previously dug trench are 
available for study. The fauna is very rich; bryozoans dominate but 
there are also brachiopods, trilobites, echinoderms, molluscs and 
conularids. All material described in this study is from the Marro- 
lithus favus Biozone, upper ‘Llandeilo Series’ (lower Caradoc Series, 
upper Ordovician, see Fortey ef al., 1995: 16), Llandeilo Limestone, 
Clog-y-fran. 
The bryozoan fauna is extremely diverse; 20 species are de- 
scribed. Trepostomes dominate with seventeen species but one 
cryptostome and two fenestrate species are also present. Four of the 
20 species from Clog-y-fran have been recognised as known species 
and two new species are also present. The other 14 could not be 
identified precisely to species level due to poor preservation or lack 
of material. These species are left in open nomenclature and are 
© The Natural History Museum, 1997 
referred to as ‘cf.’, ‘aff. and ‘sp.’ based on the recommendations of 
Bengtson (1988). 
All the bryozoans from this locality are abraded and incomplete. 
Fragments are observed in acetate peels which may be from species 
not described in this study but they are too small to attempt any kind 
of identification. 
The dominant morphological form of the fauna is erect. All but 
two of the 17 trepostome species are erect and some are branching, 
but others are impossible to tell because only incomplete colonies 
are present. The other two trepostomes have a massive hemispheri- 
cal form. This may not be a true reflection of the living bryozoan 
community, but the result of taphonomic processes. 
BIOGEOGRAPHICAL COMPARISONS 
A total of 15 genera are recognised from Clog-y-fran. All are 
cosmopolitan and have been previously described from outside south 
Wales. Ordovician bryozoans from Wales are known to have broad 
geographical ranges (Buttler 1991a). A long-lived planktotrophic 
larval stage may explain this wide dispersal (Taylor & Cope, 1987). 
Living cyclostomes have non-planktotrophic larvae but Taylor & 
Cope considered that early stenolaemates may have inherited 
planktotrophic larvae from their inferred ctenostome ancestors. 
During the Ordovician south Wales formed part of Avalonia, 
along with the Ardennes of Belgium and northern France, England, 
southeast Ireland, the Avalon Peninsula of eastern Newfoundland, 
parts of Nova Scotia, southern New Brunswick and coastal areas of 
New England (Scotese & McKerrow, 1990). Avalonia was sepa- 
rated from Laurentia (North America) by the Iapetus Ocean and 
from the Baltica by Tournquist’s Sea, both of which began to 
narrow in the early Ordovician. By the late Caradoc Avalonian 
faunas were similar to those of Baltica (Scotese & McKerrow, 1990). 
As 16 of the 20 species from Clog-y-fran cannot be precisely 
related to known taxa it is difficult to make biogeographical com- 
parisons, although Welsh bryozoans generally show the greatest 
affinity to Baltica. The four species that have been previously 
described are known from Baltica, North America and Wales. 
Hemiphragma pygmaeum is known from Sweden, Graptodictya 
bonnemai from Estonia and Russia, Hallopora peculiaris from 
Latvia and south Wales, and Eridotrypa simulatrix from Russia and 
North America 
