The lower part of the Bungonia Limestone in the Bungonia-Maruian South area, N.S.W., has previously been dated as Ludlovian. New fossil localities from the upper part of the formation yield faunas including Scabriscutellum sp. cf. S. scabrum, Schizophoria, Eospirifer eastoni and Spathognathodus sp. cf. S. remscheidensis which indicate a Lochkovian age. The Bungonia Limestone is intruded by parts of the Marulan Batholith (398 ± 7m.y.) thus giving a minimum age for the Silurian-Devonian boundary. An appraisal of published data shows that there are 20 radiometric dates with good biostratigraphic control from Silurian and Early Devonian rocks. The relationship between the palaeontolpgically-based relative duration of Silurian and Early Devonian series and stages and the radiometric age of units confined to individual series or stages, provides an estimate of the age of the base of the following: Llandoverian 433 m.y.; Wenlockian 419 m.y.; Ludlovian 412 m.y.; Pridolian 405 m.y.; Gedinnian and Lochkovian 401 m.y.; Pragian 398 m.y.; Siegenian 396 m.y.; Emsian 392 m.y.; Zlichovian 390 m.y.; Dalejan 387 m.y.; and Eifelian 383 m.y. © AAP. © 1981 Association of Australasian Palaeontologists.