Arionellus , is a disused name for a genus of trilobite. The name Arionellus was a replacement for Arionides , itself a replacement for Arion , which was preoccupied because Férussac had already used it in 1819 for a genus of slugs.
Agraulos had already been proposed as replacement for Arion by Hawle and Corda in 1847, but Barrande unjustly considered it a homonym of Agraulis, a butterfly named by Boisduval in 1836.
The species of Arionellus have now been reassigned to the following genera.A. bipunctatus = Croixana bipunctata
A. ceticephalus = Agraulos ceticephalus
A. convexus = Camaraspis convexa
A. cylindricus = Keithiella cylindrica
A. oweni = Modocia oweni
A. primaevus = Strenuaeva primaeva
A. pustulatus = Glaphurus pustulatus
A. texanus = Tricrepicephalus texanus
A. tripunctatus = Tricrepicephalus tripunctatus