Dictyonema falciferum Bulman, 1928

Rickards, R. B., Chapman, A. J., Wright, A. J. & Packham, G. H, 2003, Dendroid and Tuboid Graptolites from the Llandovery (Silurian) of the Four Mile Creek Area, New South Wales, Records of the Australian Museum 55 (3), pp. 305-330 : 315

Dictyonema falciferum Bulman, 1928

Figs. 5I, 8B , 9C , 10A

1928. Dictyonema falciferum , n.sp.; Bulman, p. 53–56, pl. 5, figs. 1–3, text-figs. 27–29.

Material. AM F114750 from F14, Bridge Creek.

Description. The flabellate appearance of this large, wellpreserved colony, some 27 mm by 40 mm, may be a preservational feature: there is a slight suggestion that it represents one half of a conical colony. The counterpart is, unfortunately, not available. There are at least 94 peripheral stipes developed, spaced at 16 in 10 mm, each with a lateral width of 0.20–0.25 mm. Branching zones are about every 1 mm proximally and 2–3 mm towards the periphery of the colony, complicated somewhat by local anastomosis. Dissepiments are spaced at 6–8 in 10 mm, possibly a little closer in places. Autothecae are denticulate but not otherwise ornamented. Bithecae are not developed with certainty, possibly rather bulbous aperturally, reflected in the slightly sinusoidal growth of the stipes when viewed dorsoventrally; the last feature is more conspicuous toward the periphery of the colony.

Remarks. This specimen differs only slightly from Bulman’s type specimens, the stipes in the Bridge Creek specimens being a little more slender on average and the thecal spacing slightly wider (15? in 10 mm compared with 16–20 in 10 mm). In most aspects our form is very close indeed to the types, which were described from the upper Llandovery (approximately crispus Biozone) of Shropshire, Wales and Scotland (Bulman, 1928: 50). This is the first record of this species from Australia.

Figures

Fig. 8. A, Dictyonema williamsae n.sp., holotypeAM F114565, F14; B, Dictyonema falciferum, AM F114750, F14. Scale bars 1 mm.

Fig. 9. A–E, illustrating contrasting stipe and dissepimental patterns in distal parts of colonies: A, Dictyonema cf. delicatulum, AM F114749; B, Dictyonema williamsae n.sp.,AM F114565,holotype; C, Dictyonemafalciferum,AM F114750; D, Dictyonemavenustum, AM F114648a, F14; E, Dictyonema paululum australis n.subsp., holotype AM F114757. Scale bars 1 mm.

Fig. 10. A, Dictyonema falciferum, AM F114750, F14; B–D, Dictyonema venustum, respectively AM F114648 and AM F114873, both BF14, and AM F114751, BF28. Scale bars 1 mm; arrow on B indicates damaged area discussed in text.