
  just a couple of imagio I thought you might find interesting. The centurio is wearing a cassus with crista transversa, the signifer (standard bearer) is wearing a bearskin over his cassus. 

 and the optio is wearing the standard crista versa 
http://erminestreetguard.co.uk/Officer%20Images/pages/Officerportraits%2001_jpg_jpg.htm follow this link, if you would, the images didn't show up.