There is a // before Thomas Mason, so he should be the first occupant of the next dwelling. Perhaps the transcriber didn't see it, and of course you will never know how well the enumerator observed the instructions at the time.
http://www.census-hel...census-abbreviations/
This is just one site where abbreviations are explained.
I too am puzzled with abbreviations such as the MB in this case - haven't found a site to explain those. In this case I can only come up with Municipal Borough.