APA (7th ed.) Citation

Marx, K., & Kugelmann, L. Letters to Dr. Kugelmann.

Chicago Style (17th ed.) Citation

Marx, Karl, and Ludwig Kugelmann. Letters to Dr. Kugelmann.

MLA (8th ed.) Citation

Marx, Karl, and Ludwig Kugelmann. Letters to Dr. Kugelmann.

Warning: These citations may not always be 100% accurate.