APA (7th ed.) Citation

Smith, H., Jones, P. L., & Harte, M. (1977). 3 great romances. Round the World Books.

Chicago Style (17th ed.) Citation

Smith, Harriet, Peggy Loosemore Jones, and Marjorie Harte. 3 Great Romances. Toronto: Round the World Books, 1977.

MLA (8th ed.) Citation

Smith, Harriet, et al. 3 Great Romances. Round the World Books, 1977.