the Upper Devonian of Iowa. 367 



ness of about twenty feet, is the uppermost member of 

 the Hackberry Stage as that formation is developed in 

 Iowa, and to it is given the name Acervularia zone from 

 its most characteristic and distinguishing fossil. 



B, VI. The Distribution of the Owen Sub-stage. 



The character of the Owen and its exposures has 

 rendered mapping of each zone impracticable. The 

 greater portion of the Owen as mapped here follows the 

 investigations of Webster, while that of the extreme 

 southern portion of Butler County is modified slightly 

 from Arey's geological map of that county. There is 

 some question as to how far north the Owen actually 

 extends, and as my studies were of a more hurried and 

 less complete character than those of Webster, I consid- 

 ered it best to rely entirely on him for the major portion 

 of the formation. There will probably be necessity for 

 revision of this portion of the map when detailed and 

 exact studies of the distribution of the Owen in the north- 

 ern counties are made. 



C. The Fossil Organisms of the Hackberry Stage. 



It is impossible to give here a complete list of the fossil 

 species that have been found in the Hackberry, as there 

 are large numbers that are apparently undescribed and 

 many more that have not yet been satisfactorily identified. 

 In my own collections are several species that I am quite 

 sure are undescribed, and the same is true of the collec- 

 tions of C. Herbert Belanski, or Nora Springs, Iowa, of 

 the University of Iowa, and of Clement L. Webster, of 

 Charles City, who possesses the most complete represen- 

 tation of the Hackberry fauna and flora that is to be 

 found. The collections of some museums, as the Walker 

 Museum of the University of Chicago, the American 

 Museum of Natural History, and the U. S. National Mu- 

 seum also contain undescribed Hackberry material, but 

 nothing, probably, that is not represented in the col- 

 lections of Webster, Belanski. and the writer. 



This list is, therefore, of such a character that it prob- 

 ably includes most of the identified species from the 

 Hackberry ; some of the most striking or most prominent 

 of the unidentified forms, and a number of the species 

 that are apparently undescribed. In order to make more 

 clear the f aunal characters of the divisions here made in 



