Morphology of Aulacoseira distans (Ehrenb. ) Simonsen var. nivalis (W. Sm. ) E. Y. Haw. from Kama-numa, Fukushima Prefecture

Abstract

Aulacoseira distans (Ehrenb. ) Simonsen var. nivalis (W. Sm. ) E. Y. Haw. from Kamanuma (Kama Pond), northern Fukushima Prefecture, Japan is 8.5-17.5 lam in diameter,4-7.5 p. m in height. Striae are arranged straight or slightly spiral,12-16 in 10 [im. Valve face has areolae which are always larger in diameter than those of the mantle. Spines are located on the top of every interstria. Single rimoportula located at the end of one row of areolae, inner shallow ringleist, extending over ringleist. Inner valve face/mantle junction has very thin silica wall.