Charge of tax where beneficiary shares are unknown results in maximum marginal rate unless limited association rate exceptions apply. Income of representative assesses is taxed at the maximum marginal rate where no beneficiary or beneficiary shares are specifically receivable or where shares are indeterminate, unless the beneficiary and their share are expressly stated and identifiable in the court order, trust instrument or wakf deed; specified exceptions permit taxation at the rate for an association of persons for limited family, testamentary, bona fide pre 1970 trusts and bona fide employee funds.