Subject: File No. Equity Market Structure 2013
From: Sal Arnuk
Affiliation: Themis Trading

October 17, 2013

Dear Sirs,

The order cancellation data, while valuable, would be much more valuable if it distinguished between order cancellations at or near the NBBO, as compared to away from the NBBO. The incidents of flickering quotes near the NBBO are much more valuable from a policy standpoint than the instances of such flickering 5% ,8%, or 10% away from the NBBO. Averaging can mask the importance of this metric.

Including this data on the website would be most valuable and appreciated.

Sal Arnuk
Themis Trading LLC