In this paper the author described the pineal body in the walrus and in Phoca vitulina and Macrorhinus leoninus, in which animals, but more especially in the walrus, it is of larger size than is usual in mammalia. In one walrus it measured 30 mm. (1.18 inch) in length and 18 mm. (0.7 inch) in its greatest transverse diameter; in another it was 29 mm. long, 13 mm. broad, and 13 mm. in vertical diameter. It rested on the superior vermiform process of the cerebellum, and was visible between the two diverging hemispheres of the cerebrum when the brain was looked at from above. [The paper is printed in extenso in the Journal of Anatomy and Physiology, January 1888, and as a part of the ‘Report on the Seals’ collected by H.M.S. ‘Challenger,’ Part LXVIIL, 1888.]