In a limited company, the liability of members or subscribers of the company is limited to what they have invested or guaranteed to the company.
The current President pro tempore of the Senate is Utah Republican Orrin Hatch. Elected on January 6, 2015, he is the 90th person to serve in this office.
So the Senate elects a President pro tempore, currently Daniel Inouye (Democrat of Hawaii) who is basically a much less powerful version of the Speaker of The House (Since the Senate doesn't have formal rules for debate the Senators themselves more or less determine their own speaking time).