Arionellus Barrande, 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]