Figure D D.1 and D.2: Yochelcionella and Helcionella are
small Middle Cambrian monoplacophorans from Australia,
ranging in size from about 4 to 7 mm.D.3 and D.4: Dyeria and
Lophospira are Ordovician gastropods from Ohio and New
York, about 30 mm in size. D.5 and D.7: Fossil and extant
cephalopods. D.5: Reconstruction of the curved Upper Silurian
genus Glossoceras from Sweden; part of the shell has been
cut away to show the chambers and siphuncle, about 25 mm in
size. D.6: The coiled Middle Cretaceous ammonite Falciferella
from England, about 25 mm in size. D.7: The living coiled
shelled genus Nautilus from New Caledonia, about 150 mm
in size.