Abstract'Clinobarylite', BaBe₂Si₂O₇, was defined as a monoclinic dimorph of orthorhombic barylite. Subsequently, its crystal structure was also proved to be orthorhombic, differing from barylite in terms of the space group symmetry,Pmn2₁instead ofPmnb, and in unit-cell dimensions. Through the order-disorder (OD) theory, the polytypic relationships between 'clinobarylite' and barylite are described. 'Clinobarylite' corresponds to the MDO₁polytype, with unit-cell parametersa= 11.650,b= 4.922,c= 4.674 Å, space groupPmn2₁; barylite corresponds to the MDO₂polytype, witha= 11.67,b= 9.82,c= 4.69 Å, space groupPmnb. The re-examination of the holotype specimen of 'clinobarylite' confirmed its orthorhombic symmetry. Its crystal structure has been refined starting from the atomic coordinates calculated for the MDO₁polytype and the refinement converged to R₁= 0.0144 for 929 observed reflections [F_o> 4σF_o]. Owing to their polytypic relationships, 'clinobarylite' and barylite should be conveniently indicated as barylite-1Oand barylite-2O, respectively; the name 'clinobarylite' should be discontinued. This new nomenclature of the barylite polytypes has been approved by the Commission on New Minerals, Nomenclature and Classification of the International Mineralogical Association (IMA 13-E).