Palaeoconchocelis Campbell, Kasmierczak et Golubic, 1979

Diagnosis: The thallus is endolithic within a calcareous substrate (crinoid columnals). The boreholes conform closely to the organism. The thallus is composed of: (1) large uniseriate filaments consisting of isodiametric or slightly elongate cells, 7-30 μm wide and 60-40 μm long, which branch repeatedly and form small plantlets. Branching is in all directions, and is lateral or subdichotomous, (2) fine, rarely branched filaments, 3-5 fim in diameter are attached to large filaments. The fine filaments penetrate the substrate for hundreds of microns (as revealed by borehole casts). Branching is rare, mostly near chain-like series of swellings (ca. 8 !lm wide)
along these fine filaments. Cells of the large filaments often contain one or two plump or shrivelled internal bodies. Both cells and internal bodies often contain a single dense, granular inclusion. A lentil-shaped structure occurs at the center of some cell cross-walls.