Dictyonema warrisi, Rickards, R. B., Chapman, A. J., Wright, A. J. & Packham, G. H, 2003

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 : 318

Dictyonema warrisi n.sp.

Figs. 12B , 13E–G

Material. HOLOTYPE AM F114647 a-b and PARATYPES AM F114629 b and AM F114717 , all from F14, Bridge Creek .

Derivation of name. After Dr Bevan Warris who first mapped the Angullong Syncline in detail.

Diagnosis. Unusual Dictyonema ,?conical, 3 cm long, with pronouncedly spinose autothecae, closely spaced at 28 in 10 mm; lateral stipe width 0.20–0.30 mm; dorsoventral stipe width 0.20–0.35 excluding spines which may be 1 mm long.

Description. The largest rhabdosome, possibly conical, is 30 mm long and 14 mm wide. A second, smaller (15 mm by 7 mm) specimen, possibly part of the same conical rhabdosome, crosses the first. The overlap area of the two creates an initially misleading Desmograptus appearance. On this large specimen the spinose thecae are difficult to see but are present. Dissepiments vary from fine and hairlike to more robust and irregular ( Fig. 13E ). Dissepimental spacing is about 12 in 10 mm but rather variable from place to place. The isolated stipe fragment ( Fig. 13F ) is in full profile and shows the ventral apertural spines well though not to full length. The bithecal apertures open in the angle between the autothecal aperture and the ventral wall of the next autotheca (thecae 1, 3, and 5 on Fig. 13F ). They are of Bulman’s (1928) type 4.

Remarks. Very few Dictyonema species are known with long autothecal spines. Rickards et al. (1995, p. 22, fig. 14G) illustrated Dictyonema sp. E with long, bifurcating ventral spines (see description of Dictyonema sp. 1 below). Dictyonema warrisi is distinct from that form in that the spines do not bifurcate.

Figures

Fig. 12. A, Dictyonema paululum australis n.subsp.,AM F114757, holotype, BF14; B, Dictyonema warrisi n.sp., holotype AM F114647a, F14. Scale bars 1 mm.

Fig. 13. A–D, Dictyonema muirae n.sp., respectivelyAM F114763, BF14, AM F114775, F14, holotype AM F114762, F14, and AM F114764, BF14 proximal part of colony attached to pebble of phosphate; E–G, Dictyonema warrisi n.sp., respectively AM F114647, F14, holotype AM F114717, W885 and AM F114647, F14, with stipes more proximal than E; H, Dictyonema sp. 1,AM F11475, F14. Scale bars 1 mm; shading on C indicates badly preserved area.