Hello Wayneskow, welcome to Stamp Community!
Quote:
Dorothea Dix 1844 there is a listing (b.Vert.pair,imperf. btwn. And with natural straight edge at bottom)

The sheet has a straight edge on three sides, so no problem there.
The other words, abbreviated, are 'Bottom pair imperforated between'.
So, a vertically-oriented pair of stamps, separated from the bottom of the sheet, only imperf. between the two stamps, is diffeerent than than a pair from, say, the above pictured ordinary type sheet.
No Scott cat. here, but I did have before, and I think the abbreviations are described in the front or back of the catalog.