Wave-lengths measured on coudé spectrograms of three long-period variables near maximum light allow an extreme S-type star (R Gem) to be compared with two M-type stars (R Hya and R Leo) in the AA5600-6500 region. The known bands of TiO, VO, and ScO, which are strong in this part of the spectra of the M stars, are too weak to be measured in R Gem. Conversely the bands of ZrO, which dominate the spectrum of R Gem, are extremely weak in the M stars. The only bands which are prominent in all three spectra are those of YO, and the intensity of the ƛ6132 band of this molecule appears to be a sensitive means of interpolating between types M and S.