The half-lives of 15 superallowed β+-emitters have been measured with high precision. There are deviations from the known values, especially for Sc41. A plot of log T1/2 versus log (Z/A1/3) for the mirror transitions and the 0+ → 0+transitions of the nuclei with A=4 n+2 contains breaks and irregularities, and therefore shows the effect of shell structure.