92 The Middle Devoxiax Deposits of Maryland 



stone occurs in the beds under consideration and contains both Agoniatites 

 expansiis and BactrUcs aciculatus. The former species is practically 

 restricted to the horizon of the Goniatite limestone in New York. 



A fourth element consists of 8 species that are confined to the Onon- 

 daga in New York, including Anophtheca acutipUcaia and several trilo- 

 bites. The first-named species is so abundant indeed that this member 

 may be called the zone of Anoplotheca acutiplicata. Two species also 

 are known in New York in formations older than the Onondaga. The 

 10 Onondaga and pre-Onondaga species constitute 36 per cent of the 

 species significant for correlation. 



The question may be raised whether some species have especial value 

 for purposes of correlation. The trilobites are highly plastic forms 

 usually indicating geological horizons with considerable accuracy. The 

 3 species occurring in this fauna are restricted to the Onondaga in New 

 York while a large number of trilobites found elsewhere in the fauna by 

 Kindle suggest a close relationship of the beds to the Onondaga. The 

 goniatites are also of high value for correlation because they are free 

 swimming forms that underwent rapid changes. The two species that 

 occur in this fauna are found in the Marcellus in New York, one being 

 diagnostic of the Goniatite limestone, while the other occurs also in the 

 Hamilton. 



It is thus seen that there are two conspicuous elements in the fauna, one 

 indicating a relationship to the Onondaga and the other to the Marcellus. 

 Kindle, who has studied this fauna from New York to Tennessee, em- 

 phasizes the importance of the trilobites and other Onondaga elements 

 of the fauna. Other observers would perhaps give weight to the later 

 elements of the fauna, holding that the most significant species are the 

 later migrants into the region. 



The faunal relations may be summarized in the following table : 



Kuttiber 



Total number of species and varieties 45 



Species not possessing significance for correlation 17 



Occurring in this fauna only 7 



Occurring in the Onondaga and Marcellus 8 



Relations not assured 2 



