Light (A) and scanning electron (B-I) micrographs of Sphenoderia ovoidea. (A, B) View of several specimens to illustrate variability in shape and size of the shell. (C-E) Broad lateral view of three individuals to illustrate general shape and arrangement of large and small shell-plates. (F, G) Close up view of aperture to illustrate shape and arrangement of apertural-plates and structure of the collar. (H) Detail of aboral region to show smaller oval or circular shell-plates on the shell apex. (I) Detail of shell surface to show overlapping, large shell-plates and small, oval plates in the interstices between them.