Spreadsheet gem -- way to work with a subset of rows?

The spreadsheet I’m trying to ingest is quite large, so I tried what
works with arrays:

sheet[1…20].each do |foo|
.
.
end

But that results in an error, wrong number of arguments (1 for 2)

Has anyone else come up with a way to test a subset of rows, other than
creating an extract file to work with?