It could be 'Szemiński' (that's male form, female would be 'Szemińska') but that's quite an approximate guess.
Things to consider is that 19th Century Warsaw had at different times, Prussian, Polish, Russian and again Polish local administration which along with it had different language and spellings. Also for consideration Warsaw at the time had only about a 30% Polish population - so are you 100% sure it's a Polish surname?
So there are numerous ways the surname could have been misspelled. The English spelling you have is unfortunately too far removed for a precise guess.