Pictured above are the two (2) air cleaners used by Cadillac in 1955.  Both are oil bath types.  That means there is no changeable paper element.  Air filtration was accomplished by forcing the air through a steel mesh element which rested in a reservoir of motor oil.  The unpainted element/reservoir in the picture on the left fits inside the black housing.

More often than not, folks will call the unit shown on the left a "batwing" air cleaner.  It is not.   The batwing air cleaner is shown in the picture on the right.  It gets the name from its shape.  You will notice the batwing has two (2) pods hanging down.  They house the oil bath cleaning elements.  The reason for two?  These air cleaners were available, and used on, only Eldorado models having the two 4 bbl. carburetor option.

Both air cleaners are seen on eb^ay from time-to-time.  The last 2009 starting price I saw for the normal single-carb air cleaner, also used by Oldsmobile, was $110.  The last 2009 starting price I noted for a real batwing was $1,500!