Under the light microscope, the microfossil colonies B. cf. braunii are yellow-yellow orange in color. Their shape is generally rounded to elliptical. The colonies appear rather small (~20-60 µm) and are usually not very well preserved. The typical structure of this algae consists of various cylindrical and ramified tubes that branch off of the colony center. In addition, the tubes show a gentle but distinctive increase in diameter near the distal endings, as already observed by Burns (1982) in samples of B. braunii Kützing (Fig. F1). We also observed some colonies with a fairly rectangular perimeter, which under strong magnification (800x) showed few but typical cells (autospores) with a diameter of 3-5 µm (Fig. F2).
Even though the preservation of the algal colonies is not perfect, they still have close morphological analogies with B. braunii, allowing us to refer to them as B. cf. braunii (Burns, 1982, fig. 6, p. 170, and figs. 14-16, p. 181; Batten and Grenfell, 1996, pl. 1, figs. 3, 10, 12, pl. 2, figs. 1, 2; H. Grenfell, pers. comm., 2000).