Fauna of the Morrow Group 
79 
Acanthocladia sp. 
Rhombopora lepidodendroides 
Orbiculoidea missouriensis? 
Rhipidomella pecosi 
Schizophoria resupinoides 
Orthotetes robusta 
Meekella striatocostata 
Chonetes laevis 
Productus nanus 
Pustula nebraskensis 
Pustula pertenuis? 
Pustula punctata 
Spirifer opimus 
Spirifer rockymontanus 
Platyceras parvum 
Myalina recurvirostris 
Aviculopecten hertzeri 
Aviculopecten? cf. interlineatus 
Deltopecten occidentalis 
Monopteria? sp. 
Pseudomonotis precursor 
Pseudomonotis inflata 
Pleurophorus tropidophorus 
Bellerophon crassus var. 
wewokanus 
Euphemus carbonarius 
Worth enia tabulata 
Euomphalus catilloides 
Strophostylus subovatus? 
Meekospira? sp. 
It has been suggested above that a progressive disappearance 
of the earlier type and an increasing ingress of the proemial 
facies of the fauna may be observed by a comparison of the three 
horizons of fossiliferous limestones. The question may be raised 
as to the propriety of placing the Mississippian-Pennsylvanian 
boundary beneath the Hale formation rather than above the 
Brentwood limestone with its Pentremites and Archimedes and 
beneath the coal horizon with the Potts ville flora. Noting, how- 
ever, the stratigraphic position of the f^Hy-nine species listed 
above as indicative of Pennsylvanian age, it is observed that 
twenty-two of them are recorded from the Hale formation, com- 
prising nearly one-third of the Hale faunule, and twenty-five 
have been identified from the Brentwood horizon. The faunal 
evidence therefore confirms the stratigraphic evidence in favor 
of considering the whole Morrow group as a unit and recognizing 
the unconformity at its base as marking the beginning of the 
Pennsylvanian period. 
Faunal Correlations 
In searching for the homotaxial equivalents of the Morrow 
fauna it seems useless to look to the portion of North America 
north and east from the Morrow locality. Throughout the east- 
ern and northern portions of the Mississippi valley the basal 
Pennsylvanian rocks are either much younger than the Morrow 
or were deposited under non-marine or brackish-water condi- 
tions which precluded the entrance of a marine fauna. In the 
