Cita APA (7a ed.)

Calder, A. The pregnant whale (postal). [s.n.].

Cita Chicago Style (17a ed.)

Calder, Alexander. The Pregnant Whale (postal). [s.l.]: [s.n.].

Cita MLA (9a ed.)

Calder, Alexander. The Pregnant Whale (postal). [s.n.].