there is no record of the species name "longirostrus" on either FishBase or ITIS (the Integrated Taxonomic Information System), e.g. there are NO species of any animal with longirostrus as the second part of the scientific name. Both those sites are maintained by taxonomists, and also include old scientific names that are no longer in use (synonymies). So it looks like longirostrus was never used at all.
Sorry to break it to ya, akapaul. Do you remember where you found that latin name to begin with?