Below is the statutory language for Theft by Property Lost, Mislaid, or Delivered by Mistake:

§ 3924.  Theft of property lost, mislaid, or delivered by
        A person who comes into control of property of another that
     he knows to have been lost, mislaid, or delivered under a
     mistake as to the nature or amount of the property or the
     identity of the recipient is guilty of theft if, with intent to
     deprive the owner thereof, he fails to take reasonable measures
     to restore the property to a person entitled to have it.

For more information on Pennsylvania Theft Statutes, see HERE.