ACKNOWLEDGMENTS

We thank S. Bengtson for allowing the use of the SEM at the SMNH. Specimens of Mellopegma uslonicum were derived from material collected by AVK, S. Bengtson, V. V. Missarzhevsky, S. Pelechaty, and A.K. Valkov, and were dissolved at the Geological Institute of the Russian Academy of Sciences in Moscow. Specimens of Stenotheca drepanoida were derived from material collected and processed by S. Bengtson and B. Runnegar. D. Geiger provided advice on nomenclature. P. Wagner and an anonymous reviewer provided corrections and suggested additions that greatly improved the paper; Wagner also added the last three characters to the cladistic analysis. This research was funded by a grant from NASA Exobiology (EXB04-0000-0117) to SMP. AVK received support from the NordCEE (Nordic Center for Earth Evolution) project (Danish National Research Foundation (Danmarks Grundforskningsfond)) grant to D. Canfield.