Sphaerocodium

Sphaerocodium is a fossil that represents the remains of bacteria in the phylum Cyanobacteria, often called "blue-green algae".
The species of "Sphaerocodium" recorded by the author Rothpletz could be symbiotic intergrowths of different encrusting organisms. Two genera ("Rothpletzella" and "Wetheredella") were proposed in 1948 by Alan Wood to include these forms in two species from the Silurian of Gotland. These acts have sometimes been misinterpreted as dividing "Sphaerocodium" into two genera and treating "Sphaerocodium" as a synonym of "Rothpletzella", whereas in fact "Sphaerocodium" is still considered a valid genus.
"Sphaerocodium" is characterised by having dichotomously-branching tubular filaments made of calcite, which formed encrusting masses on objects. These filaments branch in a fanlike pattern but remain in contact with each other; each filament is approximately 40-100μm wide and 30-50μ high. Filaments are not divided by septa. 
"Sphaerocodium" was formerly assigned to the now-obsolete family porostromata.
Fossil record.
This genus is known in the fossil record from the Ordovician to the Triassic (from about 460.9 to 221.5 million years ago). Fossils of species within this genus have been found in Europe, Russia, United States, Canada, China and Australia.