Dictyonema cf. delicatulum Lapworth, 1881

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 : 314

Dictyonema cf. delicatulum Lapworth, 1881

Figs. 5G, 6C

cf. 1881. Dictyonema delicatulum Lapworth ; Lapworth, p. 172, pl.

7, fig. 2a,b. cf. 1928. Dictyonema delicatulum, Lapworth , emend.; Bulman, p.

51–52, pl. 6, figs. 7–11.

Material. AM F114648a, AM F114749 and AM F114769– 71, all from F14, Bridge Creek.

Description. The best-preserved rectangular fragment of rhabdosome embraces eight stipes with several branching points, and measures 4× 8 mm. Stipe spacing is about 20 in 10 mm, dissepiments (which are conspicuous) 14–18 in 10 mm, and the autothecal spacing 20–25 in 10 mm.

Dissepiments vary from quite thread-like to a width of 0.10 mm, and are mostly disposed at right angle to the stipes. The lateral stipe width is 0.20–0.30 mm, but the dorsoventral stipe width cannot be measured in the absence of profile stipe views. There is, however, a suggestion of the autothecae, enabling a rough measurement, but the exact nature of the autothecal apertures cannot be ascertained, although one specimen ( AM F114769 ) does show thecae with a long ventral denticle or spine .

Remarks. The material closely matches Bulman’s (1928) redescription of the species, differing only in the dissepimental spacing (14–18 in 10 mm in the Australian specimens, compared with 10–12 in 10 mm in European specimens). We are, however, unsure of the exact nature of the autothecal apparatuses in our material, having established only that they are denticulate.

Figures

Fig. 6. A,B, Dendrograptus avonleaensis n.sp., respectively AM F114650 and holotype AM F114646a, both from BF14; C, Dictyonema cf. delicatulum, AM F114749, F14. Scale bars 1 mm.