The theory of the so-called D-mesons of Goldhaberet al. and Peruzziet al. is presented in some detail in the context of the theory of the differential dispersion relations of one of the simplest gaugetheoretic formulations of the weak and electromagnetic interactions-namely, theSU2 ×U1 model of Salam, J. C. Ward and Weinberg. This latter model we take for its simplicity, for the changes which experiment may force into it are not expected to modify the results of this paper in any significant way. It appears that we may have a complete picture of the D’s without introducing a new auantum number. The main quantitative result of the investigation is the prediction that, in the ordinarySU3 symmetry limit,mD=mψ/J/√e, wheree is the base of the natural-logarithm function:e=2.7183. Withmψ/J=3.098 GeV, this formula givesmD=1.879 GeV, in reasonable agreement with the observationsmD0=1.865 GeV andmD+=1.876 GeV.