Maryland Geological Survey 327 



occurring botli in the upper part of the Exogyra ponderosa zone and the 

 lower part of the Exogyra costata zone. 



Ammonites are altogether absent in the later Matawan of the Chesa- 

 peake and Delaware Canal, although Placenticeras placenta occurs in 

 limited numbers in the analogous Marshalltown of New Jersey. Scaphites 

 hippocrepis has been found on the Western Shore of Maryland in Anne 

 Arundel County and fragments, probably referable to Placenticeras 

 ■placenta. Cucull&a carolinensis, a species confined in its southern range 

 to the Exogyra ponderosa zone, also occurs in Anne Arundel County. 



The evidence for the correlation of the Monmouth of Maryland with 

 the Exogyra costata zone (Upper Selma-Ripley) of the South Atlantic 

 and Gulf states is much more direct. About eighty of the one hundred 

 and eighty-seven species listed from the Gulf (approximately 43 per cent) 

 occur in the Monmouth of Maryland. The forms restricted in their strati- 

 graphic distribution and characteristic both of the Monmouth and the 

 Exogyra costata zone include Nemodon eufaulensis, Anomia ornata, Cre- 

 nella serica, Crenella elegantula, Liopistha protexta, Crassatellites vadosus, 

 Aphrodina tippana. /Enona eufaulensis, Turritella vertebroides, with its 

 analogue in Maryland, paravertebroides, a number of species of Pleuroto- 

 mids, Pyrifusi and Liopepla, Enlrephoceras dehayi, Scaphites conradi and 

 Sphenodiscus lobatvs. This similarity, striking as it is, will doubtless be 

 rendered more so with further investigations of the Gulf fauna. Very 

 little systematic work has been published since the days of Conrad and 

 Gabb, and there is no doubt that rather a large percentage of the new 

 species described from Maryland is represented in the Gulf. The more 

 cosmopolitan character of the Monmouth molluscan faunas as opposed to 

 the Matawan is probably due to a slight increase in the depth of the water 

 and the breaking down of the barriers either of land or currents of water, 

 which may have prevented the free intermingling of the northern and 

 southern faunas. 



The correlation of the lower part of the Upper Cretaceous series of 

 Maryland with that of Texas has been established on the evidence of the 

 flora. The Eagle Ford contains a considerable fauna which is com- 

 parable to the Benton in the Western Interior section, but there is no 



