Pseudodictyonema graptolithorum

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 : 321-322

Pseudodictyonema graptolithorum (Po ě ta, 1894)

Fig. 16C–E

1894 Dictyonema graptolithorum n.sp.; Poěta, p. 196, pl. 9, fig. 14.

1957 Dictyonema (Pseudodictyonema) graptolithorum Poěta, 1894 ; Bouěek, p. 69–70, pl. 7, pl. 8, figs. 4–6, text-fig. 27a–c.

Material. AM F114753, AM F114755 and AM F114645, all from F14, Bridge Creek.

Diagnosis. Pseudodictyonema with characteristically ropy, compound stipes, a rectangular meshwork defined by stipes and robust dissepiments; stipes spaced at 14–16 in 10 mm; dissepiments 8–13 in 10 mm; stipes 0.30–0.50 mm wide; autothecal spacing about 14–15 in 10 mm.

Description. The stipes are markedly parallel and the meshwork strikingly rectangular. The largest rhabdosome in our collection is 15 mm long by 25 mm wide, probably developed from a short stem. The autothecae have isolated apertural regions at the ends of long tubes which, with numerous others, make up the ropy texture of the stipes. Despite the obvious complexity of the stipes the autothecal apertures are spaced regularly at 14–15 in 10 mm.

Dissepiments vary from very fine to quite robust and it is likely that some involve transfer of the thecal tubes from one stipe to the next. The spacing is also variable but in the range 8–13 in 10 mm. One specimen, AM F114645, has dissepiments spaced as high as 12–13 in 10 mm in places.

Remarks. The only difference between our material and the Czech types is that the types have a higher dissepimental spacing (15–16 in 10 mm given by Bou ěek, 1957); his figures 27a and 27c have much lower dissepimental spacing than given in his text (actually 5–6 in 10 mm).

Figures

Fig. 16. A, Callograptus ulahensis n.sp., AM F114760, holotype, BF15; B, Callograptus niagarensis, AM F114739, W885; C–E, Pseudodictyonema graptolithorum, respectivelyAM F114755,AM F114753 and AM F114645, all from F14. Scale bars 1 mm.