432 SLOART WELLE TK: 
not strange, then, that some elements of the Corniferous fauna 
became mingled with this Eurasian fauna as it migrated toward 
the Appalachian province. This will account for the presence 
of a considerable number of species which are common to both 
the Appalachian Hamilton and the Iowan faunas. In all cases 
these species are forms such as Cyrtina hamultonensis, Pholido- 
strophia towensts, Stropheodonta demissa, etc., which either were 
present in the Corniferous fauna, or had their nearest allies in 
that fauna. In the case of the genus Schizophoria we have an 
example of a form which was well represented in the Cornifer- 
sus fauna by the species S. propingua, but which became almost 
extinct in the Appalachian Hamilton fauna, to be reintroduced 
into the Appalachian province with the opening of Upper 
Devonian time by such species as S. éudliensts and S. striatula. 
In the Great Basin province the two Devonian faunas having 
a definite stratigraphic sequence are first, the fauna with Cornif- 
erous affinities in the lower strata of the section, and, second, 
the Eurasian fauna allied to that of the Iowan and the upper 
Devonian faunas of the Appalachian provinces. Both of these 
faunas doubtless entered the region by the same route from a 
nearly north direction. 
The value of any hypothesis proposed for the explanation 
of natural phenomena must rest upon the number and variety 
of observed facts for which it offers an explanation. The 
hypothesis that the Corniferous fauna had its origin in an Arctic 
province seems to afford an explanation for many facts relative 
to the geographic distribution and the faunal relationships of 
some of our Devonian faunas in America, and may thus stand as 
a working hypothesis which future observations will either 
strengthen or overthrow. 
STUART WELLER. 
THE UNIVERSITY OF CHICAGO. 
