Provisional assessment permits summary tax determination from a return, subject to regular assessment reconciliation and no appeal. Section 141 allowed provisional assessment of tax based on the assessee's return and accompanying accounts, mandating application of specified allowances and loss carry forwards. Partners could be assessed for their share if the firm's return was received; firms could be treated as registered or unregistered for provisional purposes based on prior assessment and registration filings. Amounts paid towards provisional assessment were credited to any later regular assessment, with excess refundable, and provisional assessments did not give rise to a right of appeal.