Reticulograptus thomasi, 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 : 328

Reticulograptus thomasi n.sp.

Figs. 22E , 23

Material. HOLOTYPE AM F114756 , only specimen, from BF28, W tributary of Bridge Creek .

Derivation of name. After the late Dr D.E. Thomas, Australian biostratigrapher and graptolite authority.

Diagnosis. Reticulograptus with striking polygonal arrangement of stipe interspaces; only autothecae and possible bithecae have been identified, with no clustering of thecae into twigs, or even single autothecal terminations; no association of autothecae and bithecae,

Description. The only rhabdosomal fragment is exquisitely preserved with many individual autothecal tubes visible. Each stipe is effectively zig-zag and connections with adjacent stipes are exclusively transfers of autothecal tubes. Autothecal apertures are sometimes associated with the transfer from an adjacent stipe, with an autotheca opening just before or just after the point where the “arriving” theca reaches its new stipe position. Some smaller tubes may be bithecae, as at the extreme left of Fig. 22E . Autothecae and the possible bithecae open close to the stipe surface. Autothecal tubes have an average diameter of about 0.10 mm and the possible bithecae 0.05 mm. Stipe width is 0.20– 0.35 mm. Stipes are compound with several elongate tubes comprising any one part of them. Branching gives an overall divergent pattern, and the interspaces are polygonal. Stipe spacing is 8 in 10 mm. Strictly speaking there are no dissepiments but the connecting bars of autothecal tubes are also spaced at about 8 in 10 mm.

Remarks. Reticulograptus thomasi n.sp. is a unique reticulograptid in its striking polygonal arrangement of stipe interspaces, although all the other biocharacters are typically reticulograptid. Only autothecae and possible bithecae have been identified, but there is no clustering of these into twigs, or even single autothecal terminations, and no association of autothecae and bithecae, all of which suggest this is a tuboid rather than a dendroid.

Figures

Fig.22.A,B. Thallograptus christoffersonae n.sp.: A,AM F114765, stipe development from basal holdfast, BF14 and B,AM F114746, holotype, F14; C, Koremagraptus obscurus n.sp. AM F114745,

Fig. 23. Reticulograptus thomasi n.sp., AM F114756, holotype, BF28. Scale bar 1 mm.