Neidium bobmarshallensis Bahls 2013, sp. nov.

Neidium bobmarshallensis Bahls, sp. nov. (Figs 56–59)

Valves lanceolate with broadly rounded, very weakly protracted apices. Valve length 60–79 µm; valve width 14.8–17.8 µm. A longitudinal line evident along each margin. Axial area straight and narrow, flaring a bit near the central area. Central area wide, rectangular, oriented diagonally to the apical axis. Central area bordered by short faint striae along valve margins. Raphe lateral, becoming filiform at the proximal ends, which are hooked sharply in opposite directions. Striae oriented diagonally across the valve face, 13–15 in 10 µm. Areolae 20–24 in 10 µm.

Holotype: — USA, Montana: Flathead County, Bob Marshall Wilderness, Dean Lake, 47.9237 o N, 113.1073 o W, elev. 2244 m, coll. L. Bahls, 23 August 1983. MDC sample 087501; holotype slide MDC P2-25-11 (Figs 57, 59) (circled holotype specimen in Fig. 57). MONTU!

Paratypes: — USA, Montana: Flathead County, Bob Marshall Wilderness, Upper Trilobite Lake, 47.9806 o N, 113.1393 o W, elev. 2012 m, coll. L. Bahls, 21 August 1983. MDC sample 087401; MDC slide P2-25-10 (Fig. 58). MONTU!— USA, Montana: Flathead County, Glacier National Park, Logging Lake, 48.7431 o N, 114.1239 o W, elev. 1162 m, coll. L. Bahls, 31 July 2007. MDC sample 404401; MDC slides 117-27 (Fig. 56), 38-28. MONTU!

Reported as: — Neidium kozlowii (Metzeltin et al. 2009: 336, pl. 102, figs 2–7); N. kozlowi var. elliptica (Foged 1981: 135, pl. XXVI, fig. 6).

Etymology:—This species is named for the Bob Marshall Wilderness in northwestern Montana.

Observations:— Neidium undulatum stat. nov. (this paper, Figs 66–68) and Neidium kozlowii (Mereschkowsky 1906: 16) have wider valves, distinctly protracted apices, and a lower stria density (10–12 in 10 µm). Valves of Neidium kozlowii var. ellipticum (Mereschkowsky 1906: 16) are elliptic, not lanceolate in shape. A population from Mongolia, reported as N. kozlowii, is very similar to N. bobmarshallensis in size and stria density and appears to be conspecific. They differ only in the degree to which apices of larger valves are protracted. Specimens from Alaska (Foged 1981) and Mongolia have a stria density of 14 in 10 µm, which matches N. bobmarshallensis but is higher than stria density in N. kozlowii.

Distribution and Ecology: — Neidium bobmarshallensis has been recorded from two lakes in the Bob Marshall Wilderness of northwestern Montana and from Logging Lake in nearby Glacier National Park. On the date the Logging Lake sample was collected, ambient pH measured 7.78 and specific conductance measured 43 µS/cm. This species has also been reported from a small pond in the Brooks Range of Alaska (Foged 1981) and from a lake and two rivers in Mongolia (Metzeltin et al. 2009).