<i>Actinocyclus ingens</i> var. <i>nodus</i> : a New, Stratigraphically Useful Diatom of the Circum-North Pacific

Actinocyclus ingens var, nodus Baldauf, n, var., is a morphologically distinct variety of the Miocene diatom A. ingens Ranray. The last occurrence of this new taxon approximates the top of the lower Middle Miocene Denticula Iauta Zone in the circum-North Pacific. Its first occurrence appears to be in the lower part of the D. fauta zone and possibly lies close to the Lower Miocene-Middle Miocene boundary.