TRANSACTIONS OF SECTION Q. 491 
2. A First Revision of the British Ordovician Brachiopoda. 
By Cuara HE. Sunvester, M.Sc. 
The author gave a summary of the present stage of her researches among 
the British Ordovician brachiopoda, and presented a table of the known species, 
with their range and geological and geographical distribution. The species in 
each genus were grouped around well known forms selected as types. 
3. New Discoveries in the American Eocene. 
By W. D. Marruew, Ph.D. 
The American Museum of Natural History since 1903 has carried on 
systematic exploration of the Eocene formations of the West. Mr. Walter 
Granger, Associate Curator of Fossil Mammals, and his assistants have 
thoroughly explored the Bridger, Washakie, Wind River, and Big Horn Basins 
in Wyoming, and the San Juan Basin in New Mexico, the stratigraphy of each 
basin has been studied, and the exact level of every specimen recorded. By 
improved technique of collecting and preparation a great number of delicate and 
fragile specimens have been preserved, and the collections are more extensive than 
all those hitherto made, representing more than 4,000 catalogued individuals. 
The Eocene formations are not lake deposits (excepting the Green River and 
the Florissant) but have been deposited in flood plains and blocked river basins. 
The material is chiefly of volcanic origin, derived from the early Tertiary vol- 
canoes of the Rocky Mountains, and distributed by streams, &c., and sometimes 
by the wind, in the mountain basins and on the plains. The ten successive faunze 
now recognised are: 
(10. Upper Uinta . : . Diplacodon Zone. 
Upper Eocene . { 9. Tee Washakie . . Hobasileus Zone. 
- 8. Upper Bridger . . UOvtntatherium Zone. 
wiridic/Hocerio < { ts Tae Brdaer - . Orohippus Zone. 
6. Lost Cabin’ . . . Lambdotherium Zone. 
Lower Eocene... 5. Lysite anthers Mir 
4. Gray Bull - .  . Systemodon Zone. 
f 3. Clark’s Fork ~ 
Paleocene . . j 2. Torrejon . ; . . Pantolambda Zone. 
| 1, Puerco . . .  . Polymastodon Zone.’ 
The Paleocene fauna does not contain the ancestors of the mid-Tertiary and 
later mammals; it is diminished in the Lower Eocene and dies out in the Lower 
Oligocene. The phyla which survived into the Oligocene or later Tertiary first 
appear in the Lower or Middle Eocene, for the most part suddenly, as if 
through immigration, The Clark’s Fork fauna is in the uppermost levels of the 
Fort Union formation of the Big Horn Basin, Wyoming, and underlies the 
Lower Eocene (‘ Wasatch’). It contains none of the types which come in in the 
Lower Eocene (Perissodactyls, &c.), while its Paleocene types are in advanced 
stages. 
rose progress has resulted in the study of the phylogeny and relationships 
of many groups, especially of the Creodonts, or primitive Carnivora, of the 
Fissipedia or modernised Carnivora, of the tenrecs, moles, hedgehogs, tree 
shrews, lemurs, of the horses, tapirs, titanotheres, rhinoceroses, chalicotheres, 
and of the early Artiodactyls, of the rodents, American Edentates, opossums, and 
other groups. The common ordinal characters of Placental Mammals are clearly 
defined in the Lower Eocene and the differentiation of the orders must have 
taken place during the Paleocene and late Cretaceous. The differentiation of 
the families of Placentals took place during the Eocene and later Tertiary. 
The modern genera date back to the Miocene or later. 
The differentiation of Marsupials and Placentals must have occurred much 
earlier than the Tertiary, possibly during the Jurassic or early Cretaceous, 
