Ribs is ribs except after you eat em and then you got a rhythm instrument (bones). But seriously, concave has a laterally concave top surface, swamped generally follows the contours of the barrel striking and has a "gull wing" section, raised generally has a "U-channel" section and stands proud of tangency with the barrels, vent is up on blocks or posts such that stuff can catch in the "vents", floating is up on posts but is only soldered or permanently attached at the breech end and secured by dovetail slots in the posts which allow the rib to expand or contract independent of the barrel(s). Churchill tapers from breech to muzzles so you get the "railroad" track illusion of greater length of barrel than you actually have. Game rib generally lower (less altitude above the barrel)than a target rib. Might be some niceties of differential elevation there that I've omitted but I'm kind of tired out from trying to remember if I actually know or should know or if I remember what someone told me or if they actually did. Don't want to go too far here and have to screw myself up into the BICBW posture.
jack
