Halamphora subtilis

Halamphora subtilis Stepanek & Kociolek sp. nov. (Figs 45–59)

Description. Valves are narrowly semi-elliptical and dorsiventral. The dorsal margin is smoothly arched near the apices, becoming flat over the center and the ventral margin is tumid. Valve length 14–18 μm, valve breadth 2.5–3.5 μm. Apices are protracted, capitate and weakly deflected ventrally. The raphe is straight, with straight to weakly dorsally deflected proximal raphe ends. The axial area is narrow throughout. Only a ventral fascia is present and extends to the margin. The dorsal striae, 21–25 in 10μm, are uninterrupted, radiate throughout and more widely spaced near the valve center. The ventral striae, 46–48 in 10μm, are difficult to resolve in LM. In SEM, the raphe is straight both internally and externally (Figs 55, 58), with the external proximal ends nearly straight (Fig. 56) and the distal ends sharply hooked dorsally (Fig. 57). The dorsal raphe ledge is prominent, composed of a thin siliceous flap running uninterrupted the length of the valve (Fig. 55, arrow). The dorsal striae are separated by thick costal ribs and are coarsely and somewhat irregularly uni- to triseriate both externally (Fig. 57) and internally (Fig. 59). The dorsal costae at center are distinctly thickened both externally (Fig. 55, arrowhead) and internally (Fig. 58, arrow). No dorsal marginal ridge is present, although striae are crossed by thin, irregularly placed intercostal ribs near the dorsal margin (Fig. 56, arrows). The ventral striae are small and fine (Figs 55, 58).

Holotype. Slide and material ANSP GC 64903, Academy of Natural Sciences, Philadelphia, USA. Holotype specimen illustrated in Fig. 46. Isotype. Slide and material JPK 8362, University of Colorado, Museum of Natural History Diatom Herbarium, Boulder, USA.

Type locality. Adobe Creek (33.51272, -117.27038), rock scrape, Riverside County, California, USA. Collected by J.P. Kociolek, November 2008.

• Author
  Stepanek and Kociolek 2013
• Length Range
  14–18 µm
• Width
  2.5–3.5 µm
• Striae in 10µm
  Dorsal striae 21–25 in 10 μm; ventral striae 46-48 in 10 μm