Halamphora latecostata

Valves are semi-elliptical, with rounded dorsal margins and nearly straight ventral margins that vary from slightly concave to slightly convex. Apices are distinctly protracted, round and subcapitate to capitate. Dorsal striae are radiate throughout, increasing from 9-13 in 10 µm near the center to 15-18 in 10 µm at the apices. Ventral striae are shortened and radiate to parallel. The ventral striae are interrupted at the center and vary little from 19-20 in 10 µm across the valve. The axial area is linear. On the dorsal side, the axial area is narrow. On the ventral side, the axial area expands near the central area. The raphe is filiform. The proximal raphe ends are inflated and deflect slightly to the dorsal side of the valve. Areolae are not visible in LM.

Patrick and Reimer (1975) used the name Amphora acutiuscula in their volume, Diatoms of the United States, for a taxon conspecific with the specimens shown on this page. Like these illustrated specimens, the Patrick and Reimer material was also collected from the Sabine River, Texas. Patrick and Reimer did not, however, examine Kützing's original material. Kützing's type material was revisited by Levkov (2009, Pl. 265), but the type of Amphora acutiuscula varies considerably from the Patrick and Reimer concept. The species Halamphora latecostata described by Stepanek and Kociolek (2013) conforms to the taxon illustrated here, and also to the taxon to which Patrick and Reimer misapplied the name A. acutiuscula.

While Levkov (2009) imaged Kützing's type material (Pl. 265, Figs. 12-15), he did not refer to this plate in his recombination of Halamphora acutiuscula, but instead referred to a Venezuelan population (Pls. 96, 109, 234) dissimilar to Kützing's type. The comparison of H. latecostata to H. acutiuscula found on this page refers to the type images only (Pl. 265).