If any land or building, bearing two or more municipal numbers, or

portions thereo fbe amalgamated into one or more new premises, the Commissioner shall on such amalgamation assign to them one or more numbers and assess them to taxes specified in section 89 accordingly: Provided that the total assessment on amalgamation shall not be greater than the sum of the previous assessments of the several premises except when there is any re-valuation of any of the said premises.