L. 3’ 3”
It is known that this pair of lions was in place by the beginning of the Civil War. There are post war descriptions of the lions being painted naturalistic colors. These types of sitting lions have long been used to “guard” entrances to houses and estates. The English as well as many countries used lions as symbols of Royalty. They are far rarer than the sleeping lions.
These lions appear as No. 544 in the Wood & Perot Catalog ca. 1870. They are the same size as the dimension given in the catalog. The engraving in the catalog is marked Wood & Perot meaning that the statue had been offer early. Wood was in partnership with Perot from 1857-1865.
The lions also appear in an engraving of the store front of the Composite Iron Works Company (aka J. B. Wickersham) in 1873 New York City Directory. While one of the sleeping lions appears in the ca. 1857 catalog of this company the sitting lion does not. 
These statues could have been influenced by the Antoine-Louis Barye (French, 1796-1875) statue done for the Tuileries gardens in Paris. 
 Gayle, Margot. Victorian Ironwork: A Catalogue by J. B. Wickersham, with a new introduction by Margot Gayle. Athenaeum Library of Nineteenth Century America, Philadelphia, 1977
 Smithsonian American Art Museum, the Luce Center. http://www.americanart.si.edu/collections/search/artwork/?id=1471