THE FAUNA OF THE MORROW GROUP OF 
ARKANSAS AND OKLAHOMA 
Kirtley F, Mather 
Introduction 
The Morrow fauna is of unusual interest paleontologically 
because of the intermingling of forms displaying a strongly 
Mississippian aspect with those of as equally strong a Pennsyl- 
vanian facies, which stamps it as transitional between the 
faunas of the two periods named. The large number of new 
species and the presence of several genera not previously known 
to occur in the Pennsylvanian formations of North America 
add to its intrinsic interest. Stratigraphically it is of import- 
ance because of the light which it throws upon the early Potts- 
ville marine life of this continent. The occurrence of a fossil 
flora of known relations between two of the fossiliferous horizons 
in the group makes possible a correlation with the non-marine 
or brackish-water formations of early Pennsylvanian age in the 
Appalachian trough; the fauna will therefore serve as a con- 
necting link between the marine Pottsville of the west and south- 
west and the contemporaneous non-marine deposits of the east 
and northeast. 
The collections made by the writer were obtained during the 
three school years 1911-1914 while a member of the faculty of 
the University of Arkansas situated at Fayetteville in the center 
of the area of outcrop of the Morrow strata. Determinations 
were made and descriptions prepared during the winter 1914- 
1915 in Walker Museum, the University of Chicago, where the 
types of all new species have been deposited. 
Acknowledgements 
It is a pleasure to acknowledge my indebtedness to L. C. 
Snider, A. H. Purdue, and R. D. Messier for the collections of 
fossils made by them, as recorded in the locality list, page 247, 
and to H. D. Miser and also Mr. Messier, for suggestions as to 
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