a1 E.R. 154 C.N.R.S., 8 Rue Buffon, 75005 Paris, France.
a2 Palaeontological Institute of the U.S.S.R., Academy of Sciences, Moscow, B 49, U.S.S.R.
a3 Geology Department, Macalester College, St Paul, Minnesota, 55105, U.S.A.
Reconnaissance geological mapping (1962–75) followed by detailed geological investigations (1979–80) in the Ellsworth Mountains of west Antarctica have established the existence of extensive Middle and Late Cambrian strata. Forms tentatively referred to Archaeocyatha have been examined by F.D. and A.R., who concluded that, despite the commonly held opinion that the phylum became extinct at the boundary of the Lower and Middle Cambrian, the Ellsworth Mountains' forms represented Irregularian Archaeocyatha which survived in protected niches into the Late Cambrian. The age of the fauna containing the archaeocyaths is firmly dated by abundant trilobites including species of Homagnostus, Pseudagnostus, Kormagnostella, Erixanium and Onchopeltis.
(Received March 29 1982)
(Revised April 27 1983)
(Accepted November 23 1983)