DEPARTMENT OE GEOLOGY 25 
Nummulites. — These are abundant and characteristic fossils 
of this period. They are shells of a Rhizopod, which in Europe 
and Africa formed limestones many thousand feet in thickness. 
A representative series of mollusc shells is shown. In both 
the univalves and bivalves a close resemblance to modern shells 
will be noticed. Most of the genera are identical with living 
forms. Such are Venus, Cardita, Area, Tellina, Meratrix, etc., 
among Pelecypods, and Natica, Turritella, Cerithium, Strombus, 
Fusus, Murex, etc., among Gastropods. 
Vertebrate fossils from the Eocene, or first stage of the Ter- 
tiary period, are represented by a series of fishes from the Green 
River shales and a cast of the large horned mammal, Dinoceras 
mirabile. (Hall 60.) 
The fishes from the Green River shales include a great num- 
ber and variety of bony fishes, or Teleosts, of modern types. 
Such familiar forms as the perch, the herring, and the ray are 
included. (Hall 59.) 
Mammals of the Oligocene stage, or second subdivision of the 
Tertiary period, are represented by a great number and variety 
of forms, most of which were collected by special expedi- 
tions sent out by the Museum. (Hall 59.) These are mostly mod- 
ern types of mammals. Among those represented are the primi- 
tive cats, dogs, squirrels, rabbits, camels, tapirs, horses and rhi- 
noceroses. There are also shown a number of the older types of 
mammals which had their origin in the first Tertiary stage and 
have no modern representatives. Among these are Hyce- 
nodon, Oreodon, Elotherium, Anthracotherium, Titanotherium, 
Hyracodon, and Metamynodon. The collection includes a 
mounted skeleton of the sabre-tooth cat, Dinictis, a representa- 
tive series of skulls of the primitive dogs, Cynodictis and Daph- 
cenus, of the three-toed horse, Mesohippus, the cursorial rhi- 
noceros, Hyracodon, the more typical rhinoceros, Aceratherium, 
the large suilline, Elotherium, and the great horned ungulate, 
Titanotherium. The series of Titanotherium skulls is especially 
fine. 
Mammals from the Miocene, or third stage of the Tertiary 
period are represented by collections from two localities, the 
Deep River beds of Montana, and the Loup Fork beds of Ne- 
braska and Wyoming. They include the following forms : 
