Four new Rhoicosphenia species from fossil deposits in India and North America

Rhoicosphenia Grunow is a common diatom in both freshwater and marine ecosystems and the genus can be found on nearly every continent. Most of the currently described taxa are extant and only six of 58 taxa are known from the fossil record. Also, reports from freshwater habitats of the Indian subcontinent are rare, with one report of Rhoicosphenia marina from marine ecosystems. Rhoicosphenia is common in freshwater and marine ecosystems of the USA and three fossils have been described from the Pacific Northwest. Four new species of Rhoicosphenia are described from fossil deposits in Gujarat, India and Oregon, USA. The new species from India are R. gandhii, a large, coarsely ornamented species and R. indica, a smaller species, both found in the same fossil deposit. The species from Oregon are R. reimeri, another large taxon, as well as R. patrickae, another small species, and both are found in the same fossil deposit. These new species descriptions highlight the recent trend of discovery of Rhoicosphenia diversity over the past decade. Finally, a discussion of the valvocopula structure in Rhoicosphenia is included with comparisons to septa and septum-like structures of other diatom genera.