 Shares of MarketAxess Holdings Inc. sank 5.2 in afternoon trading Wednesday, enough to pace the SP 500s decliners, after Raymond James analyst Patrick OShaughnessy said second-quarter trading volumes disappointed amid a lower volatility backdrop. OShaughnessy reiterated the outperform rating hes had on the stock for at least the past 16 months, but cut his price target to 530 from 580 after volumes finished lower than he had previously projected, as industry wide volumes and the companys market share continued to face headwinds in a lower volatility backdrop. 