Cyclograptus, Spencer, 1884

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 : 328-329

Cyclograptus ? australis n.sp.

Fig. 21B

Material. HOLOTYPE AM F114651 , from BF28, Bridge Creek .

Derivation of name. To record the possible occurrence of the genus in Australia.

Diagnosis. Cyclograptus ? with thecorhiza; 32 peripheral stipes some 6 mm from thecorhiza; autothecal apertural regions clearly isolated; autothecal diameter 0.15 mm and spacing approximately 18–20 in 10 mm; bithecae possibly present as thin tubes in thecorhiza.

Description. The single rhabdosome has a “basal disc” or thecorhiza 7 mm wide, possibly incomplete, from which about ten stipes arise. These bifurcate quite quickly, and then divide again in some cases, resulting in 32 peripheral stipes some 6 mm from the thecorhiza. The rhabdosome appears to be incomplete although its general shape is clear. The stipes consist of bundles of long thecal tubes, and in several places the autothecae can be seen opening in isolated fashion, sometimes slightly bent ventrally. Their diameter is 0.15 mm and the autothecal spacing approximately 18–20 in 10 mm. The autothecal apertures appear to be unadorned by processes or spines except, possibly, a slight extension of the ventral lip. Long thecal tubes can be detected in both the thecorhiza and in the up-growing stipes, but the termination of the stipes is usually by a single ventrally-curved autotheca. Bithecae may be present as thin tubes in the thecorhiza but this is not certain. The stipes may be unbranched, may branch after one third of their length, occasionally after two thirds of their length, and two stipes branch three times.

Remarks. The thecae are unknown in any described species of Cyclograptus , other than as bundles of elongate tubes in the thecorhiza and stipe. In C.? australis n.sp. the autothecal apertural regions are clearly isolated. The type species, C. rotadentatus , also exhibits stipes terminating in a single autotheca, but is more regular in its branching than C.? australis. Cyclograptus scharyanus ( Göppert, 1860) has a stem-like structure, unlike other cyclograptids. Cyclograptus irregularis Bouěek, 1957 is a much more robust species with broad stipes, and C. multithecatus Bouěek, 1957 has more compound stipes than C.? australis. All previously described species of Cyclograptus are Wenlock (Silurian) whereas our specimen is late Llandovery. The presence of a thecorhiza in C.? australis with masses of thecal tubes, suggest the tuboid Cyclograptus but the stipe branching pattern seems greater than in other cyclograptids except perhaps C. multithecatus .

ACKNOWLEDGMENTS. We are most indebted to Dr Chris Jenkins for making available his collections and maps, and for discussing this project with us at various times. Graptolite collections made by Drs Jenkins and Warris were borrowed from the School of Geosciences, University of Sydney with much-appreciated assistance from Dr Tom Hubble. Property owners in the Four Mile Creek area, particularly Ken Williams of “Ashburnia”, Tim Christofferson of “Avon Lea”, David Hughes of “Glendalough”

and Sinclair Stratton of “Ulah” have most graciously allowed free access to their properties and given guidance and assistance. Dr Ian Percival and Ms Lucy Muir are thanked for their assistance in the field in November, 2000. R.B.R. would like to record his thanks for financial support to Emmanuel College, Cambridge, the Department of Earth Sciences, Cambridge (Cowper Reed Fund Managers), the Royal Society, and the University of Cambridge. A.J.W. records his sincere gratitude for support by: the School of Geosciences and the SERC research group, University of Wollongong; the Betty Mayne research fund, administered by the Linnean Society of NSW: and Emmanuel College, Cambridge for the award of a Quartecentenary Visiting Fellowship during Lent Term, 2001. GHP collected in the 1950s and 1960s with financial assistance from the Department of Geology and Geophysics, University of Sydney.