It shall be the duty of the auditor, immediately upon the reception of the claims certified to him by the county clerk, to proceed to examine and audit the same, and on or before the first Monday of the next succeeding month to certify to the county clerk his report and decision on the claims before him, stating in proper form the specific amount allowed by him, to whom allowed, with a memorandum stating under what law and by virtue of what contract such amounts are allowed; and where claims are not allowed by him, or when they are partially allowed, the reasons therefor shall also be stated in the report; and all claims certified by the county clerk to the auditor shall be reported by the auditor on or before the first Monday of next succeeding month after their reception by him.