MARYLAND GEOLOGICAL SIHVKY 87 



The following species of the Aquia stage, on the otiier hand, have not 

 been found below the I'ltper ("hickasawan, viz.: 



FutuK intent riiiliiM Heilprlu. Pectcn r/iocturennin Aldricli. 



Lucinu itfikri Clark. Pterin llmnia (ConradK 



Modiolus alabaineitti» AldricL. 



Of these, Pleria limiila also occurs in tiie C'lailxjrniaii. The Aquia 

 stage also contains several species that have not been found Ijelow the 

 Claibornian in the Gulf. They are: 



Mesalia rjfjrutii (Conrad). Corhnfa ouincuii Conrad. 



(/j OdoKtomia tritpaquara (Harris). 



The following species occur in the Jack.sonian, viz.: 



Cfiduhi* abruptnn Meyer and Aldricli. Pecten dalli Clark. 



Corbtda oniitctt* Conrad. Oxtrea iO>jphaeontrea) vomer (Morton). 



Xone of them is of special significance. 



Before final conclusions are drawn from these comparisons, however, 

 the fact must be taken into consideration that the Maryland beds have 

 probably been examined at the present time more thoroughly and at a 

 greater number of localities within the same limited area than those of 

 the Gulf, and that some of the forms above mentioned may be shown 

 upon further study to have a wider range in the Gulf than has been 

 given to them. Due allowance must also be made for differences in judg- 

 ment in the identification of species. At the same time, it is ver}' clear 

 that the species common to the Gulf and Middle Atlantic Slope differ 

 materially in their geological range. This is evidently due in part to 

 the difference in physical conditions in the two areas and also in part 

 to migration. But after taking these facts into consideration it will 

 be seen that the fauna of the Aquia is much more closely related to the 

 Chickasawan as a whole than to either the Midwayan or Claibornian and 

 that there is a somewhat closer resemblance to the Lower than to the 

 Upper Chicka.sawan. The distance, however, between the two areas, 

 the difference in pjhysical conditions and the possibilities of migration 

 are too great to admit of any attempt to draw exact parallelism between 

 the substages. 



Nanjemoy Stage. — The Xanjemoy stage contains the following species 

 found in the Lower Chiekasawan of the Gulf, all but one of which 

 (CucuUaea gigantm) also range on upward into the Upper Chiekasawan 

 or higher stages. They are: 



