New inclusions found in Baltic amber allow to distinguish and describe new species of Rhabdomastix – Rhabdomastix hoffeinsi sp. nov. and provide a comparison of atypical wing venation of chosen species of this genus collectively reffered to as a group ‘R. caudata’. A new species of Rhabdomastix was determined herein with particular description and diagnosis, complete set of drawings and photographs. Thanks to new discovery, an attempt was made to explain the complete or partial preservation of crossvein r-r (R₂) in the ‘R. caudata’ group of craneflies and disscuss including the Eocene species Rhabdomastix klebsi in this group. New results give us possibilities to interpret that craneflies of ‘R. caudata’ group probably occured in fauna already in the Eocene, there is no evidence of their existence on Earth before.