Hallowell's Firearm Dictionary definition of a swamped rib ...............

Swamped Rib - A minimalist, smooth, concave, practically hidden, top rib on a side-by-side gun that connects the two barrels together, but provides no obvious extra aid to pointing---leaving the whole silhouette of the barrels themselves as the shooter's frame of reference. Photo


The photo shows a full length, concave rib.

May God bless America and those who defend her.