Twitter’s (TWTR) first-day market cap would place it among the largest 200 companies in the S&P 500, and the stock so far this week got two new hold ratings. Twitter closed its first day of trading Thursday at 44.90, which would have given it a market cap of about $24.5 billion. “It would rank No. 164 in the (S&P 500) index overall, ahead of companies in more ‘traditional’ industries,” FactSet Research points out in a blog post . It’s a bit lower