The rigid Cheilostomes which have this habit were formerly placed in the genus Eschara, but the bilaminar type is common to a number of genera, and there can be no doubt that it is not in itself an indication of affinity.
The body-wall is extensively calcified in the Cyclostomata and in most Cheilostomata, which may form elegant network-like colonies, as in the unilaminar genus Retepora, or may consist of wavy anastomosing plates, as in the bilaminar Lepralia foliacea of the British coasts, specimens of which may have a diameter of many inches.
In Flustra and other forms belonging to this type, the zoarium is accordingly flexible, and either bilaminar or unilaminar.
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