Illustrating sexual differences in horns.

Base of male horns greater in circumference than those of females, regardless of relative length.

• Fig. 1. Ceratotherium simum simum, female, old; from South Africa; exact locality not known ; specimen in the department of paleontology at the American Museum of National History.

Type of abnormal projecting horn found only in some females; horn projecting forward at greatest possible angle, the tip when feeding coming in contact with the ground and showing a flat, worn surface on its outer face.

• Fig. 2. Ceratotherium simum cottoni, female, adult; from Rhino Camp, Lado Enclave ; shot by Kermit Roosevelt, January 21, 1910. No. 164594, U. S. National Museum.

The longest horned specimen secured by the expedition and the only one having the forward pitch and wear on outer surface of tip as in fig. 1 ; length 29^ inches.

• Fig. 3. Ceratotherium simum cottoni, female, immature ; from Rhino Camp, Lado Enclave ; shot by Col. Theodore Roosevelt, January 10, 1910. No. 164587, U. S. National Museum.

• Fig. 4. Ceratotherium simum cottoni, male, immature ; from Rhino Camp, Lado Enclave; shot by Col. Theodore Roosevelt, January 15, 1910. No. 164635, U. S. National Museum.

Longest male horn secured by the expedition ; length 24^ inches.

• Fig. 5. Ceratotherium simum cottoni, male, adult; from Rhino Camp, Lado Enclave ; shot by Kermit Roosevelt, January 20, 1910. No. 164593, U. S. National Museum.