. Bulletin of the British Museum (Natural History), Geology. . Fig. 136 'Glyptograptus dentatus (Brongniart 1828). Well-preserved small rhabdosome, x 5, and detail of its proximal end, about x 20, early Llanvirn, D. artus Biozone, loc. 50, Llanfallteg Formation, Q5810. Fig. 137 'Glyptograptus austrodentatus Harris & Keble 1932. Typical specimen, Llanfallteg Forma- tion, early Llanvirn, D. artus Biozone, loc. 50, x 10, Q5803. Diagnosis. See Bulman, 1963: 673-675. Discussion. Bulman (1963) revised G. dentatus, and further description of isolated material was given by Skevington (1965). Elles
. Bulletin of the British Museum (Natural History), Geology. . Fig. 136 'Glyptograptus dentatus (Brongniart 1828). Well-preserved small rhabdosome, x 5, and detail of its proximal end, about x 20, early Llanvirn, D. artus Biozone, loc. 50, Llanfallteg Formation, Q5810. Fig. 137 'Glyptograptus austrodentatus Harris & Keble 1932. Typical specimen, Llanfallteg Forma- tion, early Llanvirn, D. artus Biozone, loc. 50, x 10, Q5803. Diagnosis. See Bulman, 1963: 673-675. Discussion. Bulman (1963) revised G. dentatus, and further description of isolated material was given by Skevington (1965). Elles & Wood (1907: fig. 174; pi. 31, figs 4b-d) have already illustrated material from the Llanvirn part of the Llanfallteg Formation (misspelled 'Llanfanteg' on their p. 254). This is often well preserved, in full or partial relief. The species is distinguished from G. austrodentatus particularly by the sharp upward growth of th l1 and th l2, with a stout virgellar spine. Specimens conforming to Bulman's sensu stricto usage of dentatus are numerous in the latest Arenig and earliest Llanvirn. The earliest biserials in Wales, and probably as old as anywhere, are from the Bergamia rushtoni Biozone. These include (Fig. 135e) a specimen which has a maximum width of 2-5 mm, and which also tapers distally. Bulman cites 2-2mm as a maximum for G. dentatus. Tectonic 'extension' is not usually evident in the Pontyfenni Forma- tion and it is believed that the wide stipe was originally so. The same horizon has also yielded a narrow specimen which widens rather rapidly to 1 -6—1-7 mm (Fig. 135d), a width which is retained throughout the rest of the rhabdosome. This form is intermediate between typical dentatus and what Bulman (1963) called G. shelvensis (with distal width 1-3-1 -5 mm) from the Shelve Church Beds, Shropshire. We have other specimens (Fig. 135j) from beds as high as Llanvirn which are only slightly wider than shelvensis, and it seems possible that shelvensis may not prove d
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