164 Tlie American Geologist. September, 1892 
the Appalachian Devonian of North America, thus indicating 
their extra-limital range in the latter region. 
In the determination of the genetic affinities of the faunas of 
the southern hemisphere with those of the lower and middle 
Devonian in North America, just as in the tracing of the affinities 
of the Tully limestone fauna and upper Devonian, it is not the 
identity of species or the majority of species in contrasted regions 
that plays the greatest part, l)ut it is the testimony of the some- 
what isolated forms, whose local distribution is traceable, and 
also by the breaks in successive lines of species which are asso- 
ciated together as races, though the species at each stage or in 
different regions may be described under different names. 
In the study of the Ouboides zone, it was such species as 
Ortliis fi/IIiensis, Stropliodontd, mucroiinta car. tidliensis, Rhyn- 
choiieUd reiiusfiila, which told the tale, each differing specifically 
from any European species, but belonging to races, which in 
Europe had representative species extending from the Silurian 
through the Devonian into the Carboniferous system, Init in the 
Appalachian region lacked representatives in the middle Devon- 
ian, though well represented in the upper Devonian of New 
York, and were represented also throughout the Devonian deposits 
in the Nevada and Iowa areas. The continuance of the Euro- 
pean type above this zone in the Appalachian region was also tes- 
tified to by such species as Spiv if era he vis and Sptrifcra dis- 
juncta, Productus dissimUls of Hall {liallianus of Walcott), 
Orthis imjircsaa, RhyachoneJht pngitHs and others, which are well 
represented in the fauna above the Cuboides zone, but have no 
forerunners in the Appalachian higher than the lower Helderberg 
(in rare cases seen in the Corniferous), while in the European 
faunas there are connecting species all through the middle De- 
vonian, thus pointing to a change of fauna, not by rxtiuctuni of 
the species, but by migration from one region to another. Just 
as the presence of the bones of Mylodon, Megalonyx., and the 
tapir in the United States, now extinct in North America, indi- 
cates a former extension of the South American living fauna of 
mammals into this continent. 
It was by a similar method that Dr. Ulrich traced the historical 
relations of the Hamilton fauna of the Appalachian province in 
eastern North America to the southern hemisphere. In his de- 
scription of the Bolivian fossils collected l)y professor Steinmau. 
