(a) A bank is exempt from the definition of the term “dealer” to the extent that it engages in or effects riskless principal transactions if the number of such riskless principal transactions during a calendar year combined with transactions in which the bank is acting as an agent for a customer pursuant to section 3(a)(4)(B)(xi) of the Act (15 U.S.C. 78c(a)(4)(B)(xi)) during that same year does not exceed 500.

(b) For purposes of this section, the term riskless principal transaction means a transaction in which, after having received an order to buy from a customer, the bank purchased the security from another person to offset a contemporaneous sale to such customer or, after having received an order to sell from a customer, the bank sold the security to another person to offset a contemporaneous purchase from such customer.