Age of the hexactinellid beds of the Roberts Mountains Formation, Snake Mountains, Nevada, and additions to the Silurian sponge fauna

Abstract

The graptolite, Bohemicograptus bohemicus tenuis (Bouček, 1936), was collected with additional hexactinellid sponges from the Roberts Mountains Formation in the Snake Mountains of Elko County, Nevada, and dates the sponge beds as Ludlovian. To the modest fauna of hexactinellid sponges described by Rigby et al. (1991), can be added the new sponge genera and species Divaricospongia dilata and Fistellaspongia inclinata. The new species, Gabelia intermedia, is intermediate in size between the moderately fine-textured Gabelia pedunculus Rigby and Murphy, 1983, and the large Gabelia giganta Rigby et al. 1991. Additional specimens of Gabelia pedunculus were collected in association with well-preserved specimens of Gabelia fasiculata Rigby et al. 1991, which show additional skeletal and canal details. Associated coarse root tufts and patches of protosponge skeletal mesh were also discovered as part of the new collections and are described here, although not generically nor specifically identifiable.