Comment Letter on Joint Industry “Limit Up-Limit Down” Proposal: File No. 4-631

MFA submitted comments to the SEC on the joint industry national market system market-wide limit up-limit down plan. MFA believes that a limit up-limit down mechanism is preferable to the current single stock circuit breakers. In our letter, we raise some important concerns for the Commission and trading centers to consider with respect to the application of a limit up-limit down mechanism to the equity markets in order to avoid market disruptions and other unintended consequences under the joint industry plan. In particular, while the proposed trading limits may operate in markets with large volumes and small spreads, we are concerned that the trading limits may create disruptions when applied to smaller, less-active instruments.