Abstract New diagnoses for the morphologically closely related species Lathys humilis (Blackwall, 1855) and L. nielseni (Schenkel, 1932) are provided. These species are most easily distinguished from one another by their abdominal patterns. Detailed illustrations are provided, and the distribution limits and habitat preferences of both species are discussed. Previous records of L. humilis from Finland refer to L. nielseni. The taxonomy of the genus Lathys is also briefly discussed.