A CIRCUM-INSULAR PALAZOZOIC FAUNA. QIs; 
reaching.* Many species became extinct and many new ones 
were initiated, while several genera appear here for the first time.. 
The most important of these new genera is Productus, which 
attained at its period of initiation almost its complete range of 
primary differentiation. In the Chouteau Limestone occur 
species of this genus which represent the three subdivisions, 
including the greater number of all its known species, 2. ¢., the 
groups of P. semireticulatus, P. cora and P. punctatus. The genus. 
Productus is one of the most characteristic of Carboniferous 
time. 
It is of interest and value, for purposes of correlation to 
trace the further migrations of the fauna of the West Devon- 
jan province. When the land barrier was permanently removed, 
one detachment migrated eastward into New York and gave 
origin to the faunas of the Chemung epoch. In the Chemung 
fauna the same two elements exist as in the Chouteau fauna, but 
the western and European element isso much in the ascendancy,, 
that the fauna has avery different aspect. It seems that the 
foreign fauna was much better adapted to the conditions of 
environment than the native one, and so, instead of a general 
mixture of the two, such as took place on the shores of the 
Ozark Island, the native fauna was driven out by the foreign one, 
only a small element of it being absorbed. 
In the very base of the Chemung? are two extremely inter-. 
esting species, Rynchonella (Pugnax) acuminata, Martin, and. 
Productella hallana, Walcott. These same two species also occur 
‘It is not the intention of the author to convey the idea that the fauna of the 
Mississippian Series originated exclusively on the shores of the Ozark Island. On the 
shore of the mainland adjoining, the same opportunity for the intermingling of the 
two faunas existed. The Chouteau fauna is alone treated in the present paper because 
it is this fauna with which the author is familiar. The whole subject of the origin and 
evolution of the Mississippian faunas involves a detailed study, not only of the Chou- 
teau and Kinderhook faunas and their successors, but also of the Waverly and Mar- 
shall faunas of Ohio and Michigan. It is believed that the key to the whole problem. 
is to be found in the dual origin of the faunas as set forth in the present paper. 
2On aremarkable Fauna at the base of the Chemung Group in New York. H. 
S. Williams. Am. Jour. Sci., Vol. XXV., p. 97 (1883). Fauna ofthe Chemung Beds. 
at High Point. J.M. Clarke. Bull. U.S.G.S. No. 16., p. 72 (1885). 
