128 GEORGE H. GIRTY 



the territory they cover, and the varying conditions of the time and 

 the place. The truth of this statement will be appreciated upon a 

 consideration of the Mississippian series of the Upper Mississippi 

 Valley and the subdivisions which have been established in it. 



When we speak of the variety of conditions under which the 

 sediments in question were laid down, and remember that they include 

 the great coal deposits of this era, we are led to inquire whether the 

 faunas are marine or fresh water, or perhaps both, with the important 

 difference in facies which such difference in habitat would doubtless 

 entail. Fresh-water faunas, or at least fresh-water genera and species, 

 have been recognized elsewhere in the Carboniferous, notably in the 

 Coal Measures of England and the Permian of Russia. In North 

 America, although we have a facies which appears to be non-marine, 

 there are no Carboniferous faunas which in my belief can be called 

 fresh water. The facies in question recurs frequently, particularly in 

 the Appalachian region, and manifests little change in its general 

 aspect, although appearing at widely different horizons in the Pennsyl- 

 vanian. It is very restricted in variety though often abounding in 

 individuals. A moUusk probably identifiable as Naiadites elongatus 

 Dawson is a characteristic feature. Ostracods are also abundant, and 

 the large bivalve Crustaceans, Estheria and Leaia, sometimes occur. 

 Spirorhis is another type frequently met with, while fish scales, frag- 

 ments of Limuloid Crustaceans, and wings of insects are rare. Usually 

 this peculiar assemblage of forms is associated with abundant coal 

 plants. 



The genus Naiadites was described by Dawson from the Nova 

 Scotia Coal Measures, in which it occurs with a fauna similar to that 

 sketched above. Dawson regarded the sediments and faunas as 

 representing fresh-water conditions, and considered Naiadites to be 

 related to the Naiads of our fresh-water lakes and rivers. 



The fresh-water mollusks of the English Carboniferous were 

 included by Dr. Wheelton Hind under the three genera, Anthracoptera, 

 Anthracomya, and Anthrocosia in a valuable monograph published a 

 few years ago. Later, after studying specimens of Naiadites from 

 Nova Scotia, he reached the conclusion that Anthracoptera and 

 Naiadites were the same genus. 



Thus far the balance of evidence and opinion seems to be in favor 



