Nehalennia was a Celtic goddess of seafarers, fertility and abundance, according to Lesley Adkins and Roy A. Adkins' Dictionary of Roman Religion.
In Roman Britain, merchants offered vows to Nehalennia in her aspects as Venus, Cybele, or Nemesis.
Source: Review by Cornelius Vermeule of "The Temple of Nehalennia at Domburg," by Ada Hondius-Crone. American Journal of Archaeology, Vol. 60, No. 4 (Oct., 1956), pp. 463-464.