Dendroid and Tuboid Graptolites from the Llandovery (Silurian) of the Four Mile Creek Area, New South Wales
Author
Rickards, R. B.
Author
Chapman, A. J.
Author
Wright, A. J.
Author
Packham, G. H
text
Records of the Australian Museum
2003
2003-12-10
55
3
305
330
https://journals.australian.museum/rickards-et-al-2003-rec-aust-mus-553-305330/
journal article
10.3853/j.0067-1975.55.2003.1387
2201-4349
10092612
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.