AGE OF THE HEXACTINELLID BEDS OF THE ROBERTS-MOUNTAINS FORMATION, SNAKE-MOUNTAINS, NEVADA, AND ADDITIONS TO THE SILURIAN SPONGE FAUNA

The graptolite, Bohemicograptus bohemicus tenuis(Boucek, 1936), was co llected with additional hexactinellid sponges from the Roberts Mountai ns Formation in the Snake Mountains of Elko County, Nevada, and dates the sponge beds as Ludlovian. To the modest fauna of hexactinellid spo nges described by Rigby et al. (1991), can be added the new sponge gen era and species Divaricospongia dilata and Fistellaspongia inclinata. The new species, Gabelia intermedia, is intermediate in size between t he 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-preserv ed specimens of Gabelia fasiculata Rigby et al. 1991, which show addit ional skeletal and canal details. Associated coarse root tufts and pat ches of protosponge skeletal mesh were also discovered as part of the new collections and are described here, although not generically nor s pecifically identifiable.