This is the Serotta CXII Ti (CX2) as shown.  Serotta made very few triathlon / time trial bikes, and very, very few of the ones made were the Ti model.  This was probably primarily because of the eye-watering price of $4395 for the frame only.  This one has a full-carbon fork (about $300) that was painted two-tone to match the frame (an extra $200) with a $150 Chris King headset, bringing the grand total to over $5000 plus sales tax in 2008 dollars.

It is in really great shape, with the only items of not mentioned above.  I have listed it as a 56cm, but it actually has 55.5 cm stamped on the bottom bracket.  The sizing seems pretty typical for a bike in that range.  You can read all about the Serotta company online (they folded in 2013).  The CXII Ti is a unique and rare bike, and they do not change hands that frequently.  Serotta also made a steel version called the CXII, but it did not have the aero tubing that the Ti model has, and I don't think that it had the aero seatpost clamp.

I have also included some pics of the bike when it was built-up, but I am obviously only selling the frameset along with the Chris King headset and the aero seatpost clamp.  Local pick-ups are welcomed.