Halysites are confined to the Silurian, and were widespread in North America. They consist of large, meshlike colonies formed of chains of corallites joined together. To the left, you can easily make out the long chains snakeing their way through the sediments. These "chain corals" have more widely spaced corallites than in many other tabulate corals. The open areas between the chains saved the colony from having to excrete extra calcium carbonate without the benefit of adding polyps.
These chains were also connected end to end, increasing the overal strength of each corallite. This overall form maximized the distance between each corallite to lessen competition while they fed and minimalized calcium carbonate to save energy. In the photo to the right, Halysites can be seen insitu, marked as "d".
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