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Diatoms of the United States is now known as Diatoms of North America.
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GENERA starting with "u"


Ulnaria 2

  1. Narrow, elongate valves
  2. Narrow central sternum
  3. Central area present, may possess ghost striae
  4. Rimoportulae 1-2
  5. Girdle bands closed

Araphid - Valves are linear and elongate, with some species near 50 µm in length, others reaching greater than 500 µm in length. A narrow central sternum is present, with striae that meet from each side of the valve or are slightly offset. A central area may be present, varying from small and oval to rectangular and extending to the valve margins. The central area may contain “ghost striae”, or faint striae that are present over...


  1. Frustules long, cylindrical
  2. One elongated spine per valve
  3. Frustules lightly silicified
  4. Valves joined by numerous scale-like copulae

Centric - Urosolenia includes small, centric species that are lightly silicified. Frustules typically lie in girdle view. One elongated spine extends from each valve face. Numerous scale-like copulae, or girdle bands, join the two shallow valves within a frustule. Frustules of Urosolenia are fragile and are often destroyed by standard oxidative preparation for diatoms. Because of its fine structure, it is not often reported in...