It is shown that the formally correct expression of the existing theory of superfluidity, obtained for the momentum of a phonon gas in helium II, does not describe the physically real transfer of the effective mass of the phonon gas. The physically real transferable effective mass of a phonon gas turns out to be (10)^12 times less than it is considered in the existing theory. It is established that the laws of energy and momentum transformation of a massive quasiparticle in helium II differ somewhat from the corresponding laws used in the existing theory. It follows from this that if the gas of rotons with the dispersion law introduced in 1947 behaves as a whole, then it must be entirely at rest relative to the "unexcited background" in helium II. It is noted that the criterion for the superfluidity of liquid helium implicitly assumes the use of an additional hypothesis about the direction of the momentum excited in liquid helium II quasiparticle (phonon).