Dictyonema sp. 1

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 sp. 1

Fig. 13H

Material. AM F114754 from F14, Bridge Creek.

Description. One small stipe fragment shows 10–11 thecae spaced at 20 in 10 mm, each provided with two spines. It is not certain, but it seems likely, that these spines grow from the ventral region of the autothecal aperture. No traces of bithecae are visible. The dorsal wall shows the bases of 3– 4 dissepiments giving a dissepimental spacing of about 8 in 10 mm. The dorsoventral width excluding processes is up to 0.75 mm, and up to 1.25 mm including spines. It is uncertain whether the spines are formed from bifurcation of one ventral denticle, or whether two spines arise independently from the ventral apertural wall.

Remarks. Dictyonema sp. 1 differs from D. warrisi in having a wider thecal spacing (20 compared with 28 in 10 mm) and in having two thecal spines. Dictyonema sp. E of Rickards et al. (1995: 22, fig. 14G) has a bifurcating ventral process and a thecal spacing of 30 in 10 mm. This latter form is from the nilssoni Biozone (Ludlow) and the thecal spines are more like those of D. cervicorne Holm, 1890 , from the Ordovician of Scandinavia (although lacking the bulbous bithecae of that form) than those of D. warrisi .

Figures

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.