Algae of genus Dimorphosiphon

Abstract

The genus Dimorphosiphon, previously known only from the late Middle and early Upper Ordovician of Norway, is reported from the Upper Ordovician of East Kazakhstan and the North Balkhash area. Large collections were available for preparation and study in thin sections as well as etching with hydrochloric acid. A new species D. diadromum is established and differentiated from D. rectangulare HOeg on the basis of its thinner and longer thallus, occasional branching of the thallus, number and arrangement of central tubes, shape of the first order radial tubes and shape and orientation of the second order radial tubes. The age of the new species is Upper Ordovician. The genus Dimorphosiphon on the basis of this report is shown to have a very much wider geographic range and is evidently of stratigraphic importance, since it characterizes the boundary layers of the Middle and Upper Ordovician. --F. M. Hueber.