ORDOVICIAN BRYOZOA FROM THE LLANDEILO LIMESTONE 



131 



Autozooecia curve out gradually from the branch axis in the 

 endozone and change direction abruptly in the exozone to meet the 

 colony surface at 90°. Autozooecia within the endozone all have 

 very thin walls. 



The exozone is wide, with an average diameter of 1.9 mm. It is 

 recognised by a thickening of the zooecial walls and a simultaneous 

 change in zooecial orientation. Autozooecia all originate in the 

 endozone where they are rounded in transverse section, becoming 

 irregularly rounded in the exozone as seen in tangential sections of 

 the branches. Autozooecial diameters average 0.24 mm by 0.3 mm 

 within the exozone. 



Diaphragms are very abundant and closely spaced along the 

 whole length of the autozooecia. They are spaced on average 0.23 

 mm apart in the endozone, decreasing to 0.09 mm apart within the 

 exozone. All diaphragms are basal and are orally deflected at their 

 junctions with the zooecial walls. In the mid exozone of specimen 

 PD 8325 there is a large interval (0.34 mm) between two adjacent 

 diaphragms, which is found in the same position throughout the 

 colony. The first diaphragms on the distal side of this interval are 

 greatly deflected orally. In the majority of the colony, growth 

 resumes as normal after the interval; however, in some small sec- 

 tions the thickened exozonal wall terminates and is replaced by one 

 much thinner. 



Mesozooecia are present, although not abundant, and have a 

 maximum diameter averaging 0.12 mm. They originate in the 

 exozone, are oval in shape in shallow tangential sections, and 

 contain abundant orally deflected basal diaphragms, spaced on 

 average 0.05 mm apart. 



Acanthostyles are large and abundant, with an average diameter 

 of 0.05 mm and density of 14 per mm-. They originate throughout 

 the exozone, commonly extending the entire length of the exozone, 

 and can slightly indent the zooecial apertures. The acanthostyles are 

 composed of a hyaline core surrounded by steeply dipping conical 

 laminae. 



Autozooecial wall thickness averages 0.08 mm in the exozone. 

 Wall microstructure is composed of inclined U-shaped laminae. 

 Zooecial boundaries are indistinct. Some zooecia (especially 

 mesozooecia) are infilled with laminar calcite close to the zoarial 

 surface; in longitudinal section this infilling consists of broad U- 

 shaped laminae. 



Remarks. This species is characterised by the ramose colony 

 form, thin autozooecial walls and rounded apertures in shallow 

 tangential section. Oval mesozooecia are present and originate in the 

 outer endozone/inner exozone. Basal diaphragms are abundant 

 throughout the colony, and large acanthostyles are abundant in the 

 exozone. 



Three species of Amplexopora have been previously described 

 from the Welsh Basin. All were described by Ross (1963, 1965) from 

 the Hoar Edge Limestone. Hoar Edge Group (Caradoc), Evenwood 

 Quarry, Shropshire, and all vary markedly from the species de- 

 scribed herein. A. thomasi Ross, 1963 is a bifoliate species with 



small acanthostyles and lacking diaphragms in the endozone. Al 

 evenensis Ross, 1 965 and Amplexopora! sp. A of Ross, 1 965 both 

 have crenulate walls, diaphragms confined to the exozone and small 

 acanthostyles. 



The specimens oi Amplexopora from Clog-y-fran are similar toA. 

 septosa (Ulrich, 1879) (redescribed by Boardman 1960) from the 

 Fairview Formation (Ashgill), Covington, Kentucky. The major 

 differences in A. septosa are the absence of diaphragms in the 

 endozone and the presence of numerous short, off-set acanthostyles, 

 as well as the long acanthostyles which occur throughout the exozone. 

 Off-set acanthostyles can be identified in specimen PD 8326, but 

 have not been recognised in PD 8325. 



Other examples of Amplexopora containing abundant diaphragms 

 in the endozone have been described by Brown & Daly (1985) from 

 the Dillsboro Formation (Cincinnafi Series) of SE Indiana; they 

 were identified as A. cf. septosa. Numerous specimens (over 150) of 

 A. septosa were collected from this formation, including a few 

 atypical specimens with abundantly spaced diaphragms in the 

 endozone. Brown & Daly (1985: 24) suggested that because the 

 specimens were similar in all other respects to A. septosa the 

 differences may be due to environmental factors. The specimens 

 from Clog-y-fran are very similar to those from the Dillsboro 

 Formation, except that the short acanthostyles are less common and 

 the diaphragms more abundant. 



Genus HALLOPORINA Bassler, 1911 



Halloporina cf. crenulata (Ulrich, 1893) 



Material. NHM PD 8315, 8394. 



Fig. 27 



Description. Zoaria erect with cylindrical branches, on average 

 4.5 mm in diameter. 



Autozooecia are parallel to the branch axis within the endozone 

 and then curve outwards gradually in the exozone to meet the zoarial 

 surface at 70°. The autozooecia within the endozone have very thin 

 wavy walls. 



The exozone is narrow with an average diameter of 0.76 mm. It is 

 recognisable by a thickening of the zooecial walls and a simultane- 

 ous change in zooecial orientation. Autozooecia all originate in the 

 endozone where they are polygonal-rounded in transverse section, 

 becoming oval-rounded in the exozone, as seen in tangential sec- 

 tions of branches. Autozooecial diameter averages 0. 1 8 mm by 0.22 

 mm within the exozone. Basal diaphragms are rare or even wholly 

 absent in the autozooecia and, if present, only one or two are found 

 in the exozone. They are all deflected orally at their junctions with 

 the zooecial walls and their laminae are continuous with the 

 autozooecial linings. 



Exilazooecia are present and originate in the exozone. They are 

 rounded in shape in shallow tangential sections, with a maximum 

 diameter averaging 0.08 mm. They occasionally contain orally 



Figs 23, 24 Monotrypa sp. 23, NHM PD 8330; longitudinal section, x30. 24, NHM PD 8329; tangential section, x30. 



Fig. 25 Amplexopora sp., NHM PD 8325: longitudinal section, xl2. 



Fig. 2(> Amplexopora sp., NHM PD 8325; 26a, longitudinal section, showing large interval between adjacent diaphragms, x35; 26b, transverse section, xl2; 



26c, tangential section, x30. 

 Fig. 27 Halloporina cf. crenulata (Ulrich 1893), NHM PD 8315; 27a. longitudinal section, x22; 27b, tangential section, x6l. 

 Figs 28, 29 Graptodictya bonnemai Bassler 1911. 28, NHM PD 8392b, longitudinal section, x30. 29, NHM PD 8389: 29a, transverse section, x55; 29b, 



tangential section, x55. 

 Fig. 30 Pushkinella sp., NHM PD 8376; 30a, tangential section, x22; 30b, tangential section, x53. 

 Fig. 31 Phylloporimi sp., NHM PD 8384; 31a, tangential section, xl2; 31b, tangential section, x22. 



