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We present light and scanning electron microscope observations on two Neidium species, N. didelta and N. rectum, described by Friedrich Hustedt from Tibet. Neidium didelta and N. rectum have external proximal raphe ends that are deflected in opposite directions, as well as the presence of lacinia and renilimbi, all features of most members of the genus. Both species have a unique combination of characters. Internally, they have coverings over the longitudinal canals and areolae that are pluriseriate, much like the situation in the genus Neidiomorpha, and unlike other Neidium taxa. The areolae at the valve margin are larger than the other areolae comprising the striae. We compare these species with taxa described by Zhu & Chen, and suggest that these taxa are later synonyms of Hustedt's species. We discuss the possible systematic affinities of these taxa within the Neidium and Neidiomorpha lineage. [ABSTRACT FROM AUTHOR]

We present light and scanning electron microscopical observations on frustules of a new species of Clipeoparvus Woodbridge et al. from Tibet. Cells are small, lens-shaped to conical, have internally occluded areolae and lack any processes. The Tibetan species differs from Clipeoparvus anatolicus Woodbridge, E.J. Cox & Roberts, the only other known species of the genus described from Turkey, by the number, size and structure of the spines on the valve face. Two morphs were encountered, one bearing spines and the other without spines, and they can occur separately or in the same frustule. This phenomenon may be an example of Janus cells within this taxon. The biogeographic distribution of this taxon is discussed. [ABSTRACT FROM AUTHOR]