expansus is one of the older trilobites of the asaphus series
the Saint Petersburg region of Russia. Coming from the Lower Ordovician
Kunda layer, expansus is believed to be the progenitor
of a large
majority of the more than 30 Russian Asaphids, including Asaphus
kowalewskii, the species with the astonishingly long eye stalks.
This scarcer of
the Russian Asaphid trilobites is a natural double.