Light (A, B) and scanning electron (C-I) micrographs of Assulina muscorum. (A-C) View of many specimens to illustrate variability in shape and size of the shell. (D-F) Broad lateral view of three individuals to show general shape and regular arrangement of shell-plates. (G) Latero-apertural view of aperture to illustrate its lenticular-oval shape. (H) Close up view of apertural region showing arrangement of apertural-plates and thin border of organic cement. (I) Detail of shell surface to show overlapping, oval shell-plates.