ArionellusBarrande, 1850, is a disused name for a genus of trilobite. The name Arionellus was a replacement for Arionides Barrande, 1847, itself a replacement for Arion Barrande, 1846, 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.[1]
The species of Arionellus have now been reassigned to the following genera.[2]
^Moore, R.C. (1959). Arthropoda I - Arthropoda General Features, Proarthropoda, Euarthropoda General Features, Trilobitomorpha. Treatise on Invertebrate Paleontology. Vol. Part O. Boulder, Colorado/Lawrence, Kansas: Geological Society of America/University of Kansas Press. pp. O207, O250, O256, O272, O278, O298, O306, O322. ISBN0-8137-3015-5.