NEW MIDDLE SILURIAN HEXACTINELLID SPONGE FROM THE MACKENZIE MOUNTAINS, NORTHWEST-TERRITORIES, CANADA

Several specimens of the small hexactinellid, Cyathophycus mackenziens is n. sp., were collected from pale brown, shaly mudstone of the Road River Formation. The sponges are of Wenlock age and were collected fro m near Avalanche Lake, Mackenzie Mountains, Northwest Territories, Can ada. The small, steeply obconical sponges have skeletons in crudely ra nked quadrules to at least third-order, with first-order openings gene rally 2 min high and 1 mm wide. Successive orders decrease in stages a pproximately half that of larger elements. A moderately irregular derm al(?) layer with circular parietal gaps is suggested in some specimens . The new species is consistently finer textured than either the type species Cyathophycus reticulatus Walcott, 1879, or the later described Cyathophycus quebecensis Dawson, 1889.