Abstract

Unusually well preserved microstructure is observable in a single specimen of the sponge Dystactospongia madisonensis Foerste for the first time. Ophiraphid(?) spicules form compact rope-like tracts in the silicified interior of a specimen from the Upper Ordovician Saluda Formation near Versailles, Ind. Canals are lined with curved spicules, oriented parallel to the canal surface, usually at angles to the length of the canals. Crepidal canals are not visible within the spicules, but this is not surprising in view of the chalcedonic preservation. The compact spicule mass has been replaced by coarsely crystalline calcite in the outer part of the present specimen and other specimens associated with it. D. madisonensis Foerste is considered a choristid demosponge.

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