I am using 

self.AddUniverse(self.CoarseSelectionFunction)

def CoarseSelectionFunction(self, coarse):
'''Take the top self.coarse_university_size by dollar volume using coarse'''
# sort descending by daily dollar volume
sortedByDollarVolume = sorted(coarse, key=lambda x: x.DollarVolume, reverse=True)

# we need to return only the symbol objects
return [ x.Symbol for x in sortedByDollarVolume[:5] ]

To get the top 5 securities with the highest dollar volume. 

What I get is 

    AAPL, EEM, FB, IWM, SPY

Which obviously includes several ETFs.

How can I filter out everything except for actual stocks? 

How can I get a Universe that corresponds with the S&P500 ?