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


Bacillaria 1

  1. Raphe positioned in the central apical axis
  2. Striae relatively coarse
  3. Cells grow in colonies, linked by their keels

Nitzschioid - The raphe of Bacillaria species is located within a raised keel. In contrast to the excentrically positioned raphe and keel of Nitzschia, the raphe of Bacillaria is centrally positioned along the apical axis. The striae are distinct and relatively coarse. Living cells form colonies. The colonies are joined by silica hooks near the keel, and these silica hooks allow the cells to slide past one another in coordinated...

Biremis 2

  1. Valves with linear margins
  2. Striae not continuous across valve face
  3. Striae chambered, open externally in circular or slit-like foramina
  4. Valve mantle with similar chambered striae

Symmetrical biraphid - Biremis currently contains both freshwater and marine species. Freshwater species possess a linear margin and bilateral symmetry, while marine species are strongly dorsiventral, with amphoroid symmetry. The striae of Biremis appear to be “interrupted” (they are not continuous), due to internal plates that cover marginal chambered striae. Internally, the striae are chambered, while externally they open in circular or...

Boreozonacola 2

  1. Valves linear, often with triundulate margins
  2. Areolae coarse
  3. Central area oval to round

Symmetrical biraphid - Valves of Boreozonacola are linear, often with tumid central and subapical margins. The raphe is lateral. The proximal raphe ends are simple, curving to the primary side of the valve. The distal raphe ends curve to the secondary side of the valve. The axial area is narrow and linear. The central area is round. Striae are radiate and are composed of coarse areolae. Voight discontinuities are often present. The genus...

Brachysira 10

  1. Valves linear to linear-lanceolate to cruciform
  2. Valve apices rounded to protracted
  3. Striae finely punctate, form longitudinal undulations

Symmetrical biraphid - Valves of Brachysira are linear to linear-lanceolate in outline. The ends of the valves, or apices, may be rounded to protracted. In general, the valves are symmetrical to the apical axis. Some specimens may have a slight, to strong, asymmetry to the transapical axis. The striae are finely punctate, and form longitudinal undulations. The raphe is straight and the axial area is narrow. In the SEM, an elevated siliceous...

Brebissonia 1

  1. Striae biseriate
  2. Proximal raphe ends relatively widely separated

Asymmetrical biraphid - Valves are rhombic-lanceolate or lanceolate and slightly isopolar. The valve face is flat and the mantle is shallow. Striae are biseriate. Robust transapical ribs are present. The proximal raphe ends are expanded and internally deflected to the primary side of the valve. The distal raphe fissure is long and bent. Internally, a prominent helictoglossa is present. Copulae are open. Brebissonia is considered to be closely...


  1. Frustules extremely small
  2. Raphe reduced

Symmetrical biraphid - Frustules are extremely small, less than 15 ┬Ám in length. Valves are broadly lanceolate, with small, capitate apices. The raphe is linear and short. The raphe is contained within a distinctly thickened sternum. Striae are slightly radiate in the center valve, becoming parallel near apices. Striae are composed of single row of 1-2 areolae, a feature visible in SEM. Externally, the proximal and distal raphe fissures are...


  1. Valve face with central areolate area surrounded by radiating striae
  2. Rimoportulae or fultoportulae absent
  3. Valve margins with small, tapered spines

Centric - Brevisira is a centric diatom, with central areolae surrounded by radiating striae on the valve face. In contrast to many centric genera, Brevisira lacks both rimoportulae and fultoportulae. The frustules of Brevisira are small, with small tapered spines on the valve margins. Within a single frustule, one valve face may be concave, while the other is convex. The valve mantle is also ornamented with areolae. Living cells...