According to California Academy Catalogue of Diatom Names, Navicula directa (W. Smith) Brebisson 1854 and N. directa (W. Smith) Ralfs in Pritchard 1861 are nomenclatural synonyms (specifically, isonyms), as both were based on Pinnularia directa W. Smith. Witkowski et al. 2000 reported this taxon as the latter
ITIS taxonomy is based on the latest scientific consensus available,
and is provided as a general reference source for interested parties.
However, it is not a legal authority for statutory or regulatory purposes.
While every effort has been made to provide the most reliable and up-to-date
information available, ultimate legal requirements with respect to species
are contained in provisions of treaties to which the United States is a
party, wildlife statutes, regulations, and any applicable notices that have
been published in the Federal Register. For further information on U.S.
legal requirements with respect to protected taxa, please contact the
U.S. Fish and Wildlife Service.