LOWER CARBONIFEROUS BRYOZOA 
quantitative taxonomic, ontogenetic and palaeoecological studies. 
However, it has been argued that the silicification process is selective 
and does not necessarily preserve all elements of a fauna (Whittington 
& Evitt 1954), and secondly, that preservation is poor and only 
retains the external features of the skeleton (Cooper & Grant 1972— 
1975, Tavener-Smith 1973, Taylor & Curry 1985). 
Both calcified and silicified bryozoan fragments are found at 
~ Carrick Lough and Sillees River, and comparison of both fractions 
: indicates that more taxa are represented silicified than calcified. This 
: probably reflects the ease by which silicified specimens are re- 
_ trieved. Some authors report excellent preservation by silica of 
_ invertebrate skeletal microstructure (Brunton 1976, Holdaway & 
Clayton 1982), and of plant vessels (Stein 1982), while Schmitt & 
Boyd (1981) noted that relict ultrastructure is commonly observed in 
_ megaquartz crystals. There is no doubt that the process of silicification 
can produce both excellent and poor preservation. Schmitt & Boyd 
_ (1981) noted that the quality of preservation is related to the timing 
of replacement: poor preservation is due to delayed replacement, 
| whereas excellently preserved fine detail is produced by immediate 
| replacement of the calcite skeleton by silica. They sub-divided silica 
| patterns into five major types, of which patterns | to 4 represent 
delayed replacement and pattern 5 immediate replacement. 
A number of randomly orientated thin sections were cut from 
silicified blocks collected from Carrick Lough. In general bryozoan 
| autozooecial chambers are infilled with megaquartz, whereas the 
| skeleton is replaced by a mixture of spherulitic chalcedony which is 
| radial in appearance, tiny sub-hedral to euhedral microquartz crys- 
tals (<20um), and occasionally some megaquartz. 
Silicification may occur in descrete steps, which will produce 
different silica styles. Initially the calcite bryozoan zoarium is quite 
faithfully replaced by euhedral and sub-hedral microquartz crystals, 
| producing a thin exterior rim that is usually fuzzy in appearance 
(Fig. 105a). As the intensity of silicification increases autozooecial 
_and vesicular chamber walls are totally replaced by spherulitic 
| chalcedony (Pattern 2 of Schmitt & Boyd 1981) (Fig. 105b). Finally, 
chalcedony pervades both the walls and the megaquartz crystals that 
infilled autozooecial chambers obliterating all original skeletal struc- 
ture (Fig. 105c). Overgrowing this ubiquitious chalcedony are found 
small rhombic dolomite crystals. In some zoaria silicification has 
/ not been totally pervasive. Where this occurs the outer laminated 
cE: (eg. in Fenestella s.l.) is replaced, with the inner granular 
tissue left unaltered. 
These silica patterns indicate that replacement of the bryozoan 
colonies in County Fermanagh was delayed. In many cases replace- 
ment is incomplete: colonies may be lightly silicified on their outer 
surfaces and not silicified internally, or else portions of branches 
may be silicified and others not. In these situations colonies are very 
delicate and easily fragmented. Rarely are zoaria completely 
'\silicified. However, where this has occurred, considerable skeletal 
detail is retained, which allows for reasonable taxonomic 
determinations and morphological descriptions. In these cases the 
silica style is that of Pattern 2. 
In total 29 genera, containing 68 species have been described from 
the Viséan of County Fermanagh. This key is an aid to their identi- 
fication. It has been necessary to construct the key in two styles: a 
multi-element dichotomous-trichotomous portion and a tabular por- 
ion. Where possible taxa are keyed out in the former, but where 
‘ 
165 
there are a large number of species in a genus (as with Fenestella s.1.) 
the latter has been used. In some cases several routes through the key 
will lead to the same taxon. No attempt has been made to designate 
the various Fenestella species to the genera erected by Morozova 
(1974). 
The key to Fenestella s.l. species and other fenestrate taxa is based 
on the findings of Bancroft (1984), Olaloye (1974), and Tavener- 
Smith (1965a, 1965b, 1971, 1973). No attempt has been made to 
check their taxonomic determinations. 
Key 
1 Autozooecia developed on obverse surface only, tripartite skeleton 
GeV eloped iraascacrceseierer ct reer reie ee cere ce ee ee ci 2 
Autozooecia developed throughout ZoariuM ...........c:ccccccseceeeeeeeeeees 26 
Dey Oaniate th CUlale meets. tect rese a eee ee ea 3 
Zoaria small pinnate or non-pinnate expansions 
Zoaria basket or cup-shaped ............ccecssereeseeeseenee 
Se LOWS Ol atozOOeCialOnlbranches ae ee ee eee 4 
More than two rows of autozooecia developed ..............cccccccceeereee 11 
fame btaniches:allthicrsalne SiZcwemnacmter se ret tte are nee enn 5 
Branches of two sizes: a few primary and many secondary ............... 
CRG Seta See sae Tracsn uni ered teem ace gaaersesiauers Ptiloporella varicosa 
See Mediantcanina presen trcreeree re rs eee ee 6 
Median carina absent ...........cccccccceeceeeeees Levifenestella undecimalis 
6 Obverse surface protected by a honeycomb-like superstructure ......... 
Rois REE PSE ET acon ems vds aaa eee acne ev ona Sees Hemitrypa hibernica 
Obverse surface not covered by a superstructure ............0.0cccccceeeee0-2e q 
7  Carinal nodes arranged in a straight lineFenestella s.1. (go to Table 34) 
Carinal nodes in two offset Zigzag COWS ..........cccccccceceecseseeseeeeeeseseees 8 
8 Fenestrules quadrate, hourglass-shaped, serving four autozooecial ap- 
(GIRS ccceacdeoosed 370200262 econsaceacboce-Ehaneonesraasaaceacesncaisedtaadie6 oasesncoacedasancas6%0 9 
Fenestrules elongate, serving 8 autozooecial apertures .................. 10 
9  Peristomes large, median carina well developed, reverse surface often 
MOGUILOSE 22 A aoeres eget fetaa pense ab oscsze se Bogen vosac eines Minilya plummerae 
Peristomes slight, median carina weak, reverse surface smooth to 
mareimallygestht Aled mewsees meee ee. ayaa eee eee Minilya nodulosa 
10 Branch margins slightly indented by autozooecial apertures, median 
carina weak, one carinal node situated at branch/dissepiment junction 
OSCE COSE CLOSE CCU BCOCE PER ERECT TE ORS onerer cee ern eee Minilya binodata 
Branch margins straight, median carina moderate, arrangement of 
carinal nodes somewhat irregular ................:c0c0eesee0e0s Minilya oculata 
11 3 rows of autozooecia, keyhole-shaped apertures ..................00c00000000- 
Seeee smoot aan Saeidegs ouaee seas ace cate Seer a oe ena cee ook Polypora stenostomata 
4—5 rows of autozooecia, oval apertures, fenestrules oval 2.50mm long 
Bec CCRS SOE GOARCCE OO AEB eer ER ECRELOE EHR CRS CICeNSSORE Polypora dendroides 
4 rows of autozooecia, peristomes around apertures, fenestrules elon- 
gates 30-47 Omi on oer ere eee: Polypora verrucosa 
WD ZO ATIUITANP IM ALC cerns ne ree aeccserseae eters rien eect vat ceases see eee 13 
ZO ATAU TIAN OM P UUM ALE eee ec oavc saa cee ee ec tessce ee az 21 
13 Lateral branches lack dissepiments .................... 14 
Lateral branches connected with dissepiments .............:ccccccccc:cceeeeees 
Seti ae Oeste cic teee vas coe eat ae ES tae Sess Heese Wa Sean Ptylopora pluma parva 
Wateral branches|coalescelmesss es ssesssee reese Septopora hibernica 
14) 2rOWSiOtautozooeciaioni branches |pesecsse-ceescsecessesescessenceseesee senses IS) 
More than two rows of autozooecia ......... Ichthyorachis newenhami 
15 1 autozooecial aperture between lateral branches ................cc00000000- 16 
2 autozooecial apertures between lateral branches ... ae Site) 
>5 autozooecial apertures between lateral branches .............c:0000e000+- 
Teste Nate cette sist ones easeeataraerrnentinscuvetetetcoeecotaee Penniretepora tortuosa 
