484 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1907. 
The Cenozoic falls into the following subdivisions: 
ITIBREMENS 208) Ses 1. Glacial epoch. 
4. Pliocene-—Example: The upper light sea sands of 
Antwerp (whalebone whales, walruses, seals). 
The marine formations of the upper Italian low- 
and (whalebone whales, toothed whales, sea- 
cows). 
3. Miocene.—Example: The lower black sea sands of 
Antwerp (whalebone whales, toothed whales, and 
seals). 
Marine deposits of the outer border of the Alps 
(sea-cows and whales). Clays ef Nussdorf and 
Heiligenstadt, Vienna (whales and seals). 
2. Oligocene—Example: The sea sands of the vicinity 
of Mayence (sea-cows). 
1. Hocene.—Example: The marine chalk of the Mokat- 
tamberg near Cairo, and of the Fayum (primitive 
cetaceans and the first Ssea-cows). 
[ Present. 
ie RertiaTny= = 322s 
The different divisions, as for example the Eocene, Oligocene, ete., 
are again subdivided into Lower Eocene, Middle Eocene, Upper 
Eocene, ete. 
EG aleAy 
Hie. 12. Hic. 118: 
Fics. 11 and 12.—Skulls of two primitive cetaceans from the lower Middle Eocene of 
Bgypt. Fig. 11. Protocetus atavus E. Fraas. Length of skull 60 cm. (23.6 in.) 5 
11a, obliquely from above; 11b, from below. Fig. 12. Eocetus schweinfurthi E. Fraas. 
Length of skull 90 em. (35.4 in.). Right side. After E. Fraas. 
While only land mammals have thus far been found in the Lower 
Kocene, the first marine mammals appear in the lower Middle 
Eocene—primitive cetaceans and the oldest sea-cows. ‘These discov- 
eries were made during the last five years in a region from which pre- 
