We present new results on EAS muon flux char- acteristics which were obtained with the EAS MSU array. Of particular interest is the EAS muon number spectrum. The EAS muon number spectrum together with the EAS size spectrum gives an additional possibility for more accurate transformation to the primary cosmic ray energy spectrum.

Extensive atmospheric showers detected by the array of Moscow State University have been analyzed. Fluctuations of the number of muons and the gradient of the lateral distribution of electrons have been investigated for showers of fixed size, and the mass composition of primary cosmic rays with energies in the range 10(15)-10(17) eV has been determined. Theoretical distributions have been computed on the basis of the updated version of the quark-gluon-string model. In agreement with our earlier results, primary cosmic rays with energies above that which corresponds to the knee point show an increased fraction of heavy nuclei.

At the Moscow University EAS array the detector pulse shapes were observed with the help of two scintillation detectors of area 4 , each separated by 23 m. The pulse shapes were analysed in EAS with a particle density of more than 10 . 13 pulses were observed in the EAS with sizes at core distances R > 200 m. Some of the pulses have fine temporal structure with secondary peaks corresponding to tens of particles. Comparison of the individual experimental pulse shapes with the pulse shapes expected for the EAS particles arriving randomly due to the average time distribution indicates the non-statistical temporal structure of the pulses.

Experimental data on the EAS muon number fluctuations obtained with the Moscow State University EAS array are analysed to derive the primary mass composition at energies before and after the knee. The mass composition before the knee (E similar or equal to 10(15) eV) corresponds to that measured by direct methods, while the mass composition after the knee (E similar or equal to 10(17) eV) is enriched by heavy nuclei.