166 The American Geologist. septpmber, i892 
that the Vifu/iua is in America isolated and al»ove the horizon of 
Lcptocoi'l'ui. whereas in the Bolivian region it is not only associated 
with Lcpfoca'lia, \n\t is common and appears also in other appar- 
ently higher zones in association with Tropidolejitax, which later 
in South America is not found associated with Lrptocoelia indicat- 
ing that the North American appearance of the t^^pe is extra- 
limital and later than its greatest dominance in South America. 
Tropidohpfus shows a different history. Tt is seen in Eui'ope 
as well as North and South America and Africa, but in North 
America it is associated with a southern origin, for while it is 
particularly a Hamilton species and of the Appalachian province 
chiefl}', it runs up into the upper Devonian of eastern New York, 
and is seen above the Cuboides zone. But it is wanting in the 
Mackenzie river basin fauna (Whiteaves, "The Fossils of the Dev. 
Rocks, etc., 1891), which is the Devonian of European- Asia. In 
the European fauna it seems to be confined to a lower horizon, 
the Coblenzien of Europe or the Looe slates, while in America it 
is more characteristic of the higher part of the Hamilton, and in 
Central New York is even a Chemung species. It is reported 
from Illinois and Iowa, but is evidently a rare form in those 
faunas, and in Nevada, where it is in the lower Devonian as it is 
in the European faunas. Thus its range in the Devonian deposits 
of the Appalachian region points to its association with the 
southern faunas and migration with them after their general 
separation from the European faunas, whose connection with 
North American areas was by way of Asia and across the Pacific 
basin after the close of the Silurian, rather than by any connection 
across the Atlantic basin. 
The other species cited in Ulrich's paper on "Fossils of Bolivia" 
support the same conclusion that there was a close relationship 
existing l)etween the Devonian faunas of South America and 
south Africa and the fauna in the Appalachian trough, reaching 
as high as the Hamilton formation, and that this general fauna 
was distinct from the European- Asiatic faunas of the same period. 
This differentiation of the lower from the upper Devonian faunas 
occurring in the Appalachian region, and tracing them to centres 
of geographical distribution in opposite hemispheres of the globe, 
throws light upon certain other imi)ortant geological problems 
■concerning the Devonian deposits of North America. 
As we follow the elaborate series of Devonian formations of 
