Upper limits at the 90% confidence level are presented for four- and f
ive-prong semimuonic decays of charm mesons. From a study of four-pron
g vertices we find B(D0 --> K-pi+pi-mu+nu)/B(D0 --> K-mu+nu) < 0.037 a
nd B(D0 --> (KBAR (892)pi)-mu+nu)/B(D0 --> K-mu+nu) < 0.043. The five
-prong vertices yield the result B(D(S)+ --> eta'mu+nu)/B(D(S)+ --> ph
imu+nu) < 1.6.