Genus Dianulites Eichwald, 1829

TYPE SPECIES. — Dianulites detritus Eichwald, 1829 [syn. of D. fastigiatus] by subsequent designation (Eichwald 1860). Lower to Middle Ordovician; Russia, Estonia.

DIAGNOSIS. — Colony turbinate, cone or horn-shaped, sometimes compound, occasionally with a conical central cavity, in some species massive hemispherical; zooecia opening on upper, distal surface of colony; colony sides comprising exterior wall; not differentiated into endozone and exozone; maculae variably developed, some monticulate. Zooecia long polygonal tubes, monomorphic or obscurely polymorphic; walls thin, indistinct, granular, inclusion-rich; styles lacking; diaphragms moderately abundant, microstructural fabric strongly radial (modified after Taylor & Wilson 1999).

OCCURRENCE. — Lower to Upper Ordovician; Europe, North and South America, Asia.

COMPARISON

Dianulites Eichwald, 1829 belongs to its own family (Vinassa de Regny 1921). It shows similarities to the unplaced genus Nicholsonella Ulrich, 1890 . These genera possess re-crystallized walls which suggest a diagenetically unstable aragonitic (McKinney 1971) or high Mg calcite composition (Taylor & Wilson 1999; Smith et al. 2006). Nicholsonella differs from Dianulites by having abundant mesozooecia and acanthostyles.