HACKBERRY STAGE OF THE UPPER DEVOisriAisf. 187 



II. F. — The Acervularia Zone. 



Above the Naticopsis Zone at Owen Grove there is a slope of 

 about twenty feet, on the surface of which are numerous fragments 

 of Hmestone bearing, among other fosdls, a new species of Acervu- 

 laria that has been variously referred to Acervularia proftinda 

 Hall, and A. inequalis H. & W. by various authors. Pachyphyllum 

 woodmani (White) is common, in at least three varietal forms; 

 Stromhodes, Alveolites, Chonophylhim, and other corals are present. 

 There are several species of gastropods, and pelecypods of the 

 genus Paracyclas; brachiopods are relatively uncommon. 



In the bed of Hackberry Creek, east of the Hackterry Grove 

 escarpment, there are large amounts of residual. material from the 

 Acervularia Zone, and it is here that the best collecting is to be 

 found. Corals are common; stromatoporoids common, but less 

 so than they would be in weathered Spirifer Zone material from 

 Hackterry Grove. Stromatoporella incrustans (H. & W.), S. 

 solidula (H. &. W.) and several apparently undescribed species 

 are among them. Both corals and Stromatoporoids are frequently 

 pierced by what seem to be borings of a large species of Cliona, 

 in no way allied to the C. Hqckberryensis of the Spirifer zone. 



II. G. — Distribution of the Formation. 



The accompanying map, made up by C. L- Webster and myself, 

 will serve to show the general distribution of the formation. I 

 am particularly indebted to Mr. Webster for data regarding the 

 Owen Substage and the questionable Hackberry- areas in Worth 

 County. His long study of the formation has enabled him to secure 

 much data that I could not, in my brief work, secure. 



in. — The Fauna of the Hackberry. 



The following list, while far from complete, will serve to giv£ 

 an idea of the fauna in general, and in its stratigraphic relationships. 

 No attempt is made to enumerate all of the undescribed species; 

 those noted are in all cases the most striking or most characteristic 

 ones. 



In the fofegoing pages considerable mention of various species 

 lias been made, and the stratigraphic relations of many forms have 

 1 een noted. In order, however, to give a staisfactory idea of the 

 hases for division'of the formation into substages and zones here 

 descrited, the following list is divided into three sections: the 



