. Bulletin of the British Museum (Natural History), Geology. ARENIG IN SOUTH WALES non 1904 Didymograptus acutidens Lapworth; Ruedemann: 683-684; pi. 13, fig. 15. 1909 Didymograptus acutidens Lapw.; Cantrill, in Strahan et al.: 30 (listed). 71931 Didymograptus acutidens Lapworth MS, Elles & Wood; Bulman: 30-31; pi. 2, fig. 13. 1934 Didymograptus acutidens Lapworth MS em. Elles & Wood; Hsu: 33; pi. 2, fig. 3. non 1947 Didymograptus acutidens Lapworth; Ruedemann: 324; pi. 55, fig. 1; pi. 56, fig. 18. 1971 Didymograptus acutidens Elles & Wood; Strachan: 14. 279 14). SM A16985; origina
. Bulletin of the British Museum (Natural History), Geology. ARENIG IN SOUTH WALES non 1904 Didymograptus acutidens Lapworth; Ruedemann: 683-684; pi. 13, fig. 15. 1909 Didymograptus acutidens Lapw.; Cantrill, in Strahan et al.: 30 (listed). 71931 Didymograptus acutidens Lapworth MS, Elles & Wood; Bulman: 30-31; pi. 2, fig. 13. 1934 Didymograptus acutidens Lapworth MS em. Elles & Wood; Hsu: 33; pi. 2, fig. 3. non 1947 Didymograptus acutidens Lapworth; Ruedemann: 324; pi. 55, fig. 1; pi. 56, fig. 18. 1971 Didymograptus acutidens Elles & Wood; Strachan: 14. 279 14). SM A16985; original of Elles & Wood 1901: pi. 2, Lectotype (selected Strachan 1971 fig. 3a. Type locality and horizon. Porth Hayog (= Porth Llauog), Ramsey Island; Llanvirn. Occurrence in south Wales. A. acutidens is abundant in the Llanfallteg Formation, appear- ing in the uppermost Arenig {Dionide levigena Biozone) and continuing into the early Llanvirn. We have recovered it from all our Llanfallteg Formation localities. Diagnosis. Slender, gently declined (130°-150°) Acrograptus, with stipes that increase very gradually from 0-4-0-6 mm to a maximum of 1-5-20mm. Thecal shape characteristic, with acute d), and apertural margin usually making an angle of slightly less than 90° to dorsal stipe margin to give acutely toothed appearance. Distal thecal spacing variable with 10-13 (?14) thecae per 10mm; th 10-15 4-3-4-5mm; t = 05mm, 6 = 30° or less. Material. Q5156-60, Q5186; NMW Discussion. The species has a slender sicula 1-3-1-5 mm long, and very thin proximal parts of both stipes (Fig. 131b) which originate slightly asymmetrically to either side of the sicula; this suggests that acutidens is correctly referred to Acrograptus. Distal stipes abound in the Llanfall- teg Formation, but proximal ends are rare. From the slow rate of distal stipe width increase it is likely that the species had stipes at least 15 cm long to attain maximum width. Elles & Wood (1901) gave a goo
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