Abstract
Epilithic algae were collected at the outflow of the Suzumeno-yu at Isobe Hot Springs, Gunma Prefecture in June,2000; at the time of sampling, the water temperature was 31C, the pH was 7.6 and the concentration of NaCl was 0.49%. Almost 100% of the co llected algae belonged to the taxon in this study. The valves of these specimens were elliptical to linear-lanceolate, and the ends were acute or rostrate. The valve length was 9-24 (30) μm, breadth was 3-5 μm and there were 13-18 striae in 10 μm. The striae were perpendicular to the raphe or weakly radiate from the valve center. This taxon resembles several taxa in Navicula (e. g. N. aquaedurae, N. arcotenelloides, and N. caterva), but appears to be a new taxon due to differences in valve form. Since we believed this species to be identical to the species recorded as Navicula sp. at Mine Hot Springs by Tanaka and Nakajima (1985), we propose the new name Navicula tanakae Fukush., Ts. Kobay. &Yoshit. nov. sp. in honor of Hiroyuki Tanaka, at first author of that study.
