Cosmic ray air shower structure measurements and measurement of density and energy of air shower muons of a wide energy range simultaneously in individual air showers by two magnet spectrographs (MDM approximately 500 GeV c^-1) are presented. The measured muon densities have been used to compare with some of the previous measurements on muon densities in air showers of nearly the same size. The measured muon densities have also been applied for distinguishing between various interaction models and between light and heavier air shower primaries. In the air shower size range 10⁴-10⁶ particles the present measurements do not provide evidence for iron primaries and the different interaction models seem not to be distinguishable by air shower observation.