Emigrantia can easily be distinguished from other trilobites by the sturdy but not inflated genal spines, that are attached at midlength of the cephalon, in combination with effaced features of the raised axial area of the head shield (or glabella).

The name of the genus is derived from Emigrant Pass, Nopah Range, California, near the collection site of many of the last of the Lower Cambrian Olenellina.

Like all other members of the Olenelloidea superfamily, the eye-ridges spring from the back of the frontal lobe (L4) of the central area of the cephalon, that is called glabella.

In Peachella the genal spines are short and bloated, in contrast with being longer than the cephalon and attached halfway down its side (or lateral margin).

[1] Emigrantia is known only from the Lower Cambrian of California (Carrara Formation, Thimble Limestone Member, Nopah Range, Inyo County).