Description: Cells about as long as broad or slightly longer than broad, deeply constricted, with a linear, closed sinus. Semicells in frontal view subsemicircular with an undulated-crenated margin, in apical view elliptic with a pair of tumours at the middle on each side. Cell wall in the median part of the semicell furnished with a series of granules which is dichotomously branched from base to apex of the semicell. Cell wall at the sides of the semicell furnished with marginal and intramarginal granules. Cell wall between median and marginal ornamentation with a broad unsculptured zone. Cell length 23–27um, cell breadth 22–26um, cell thickness circa 16um, breadth of isthmus 6–8um. Essentially, C. dichotomum is characterized by the peculiar pattern of its cell wall ornamentation, ie. a median series of granules showing a furcation from semicell base to semicell apex. By this it is readily to be distinguished by other small-sized, granulated Cosmaria. (Coesel & Dingley 2005)

State distribution in Australia, based on available literature

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