correlating Geological Formations. 427 



A manuscript catalogue, furnished me by Prof. Prosser for 

 the western Maryland region which he is now working up, 

 contains . every one of the standard list of ten —there are 132 

 entries. 



On the basis of these facts it is evident that there is a 

 limited geographical extension of the fauna; as we follow it 

 southward west of the Cincinnati anticlinal, it becomes con- 

 siderably modified ; the Iowan area and the northern exten- 

 sion of the Devonian across central British America neither 

 contain the Tropidoleptus fauna, although they do contain a 

 fauna which is believed to be of Meso-Devonian age. The 

 affinities of the Meso-Devonian faunas in Iowa and the Mani- 

 toba-Saskatchewan region (as I have previously suggested*) are 

 more closely akin with the European Devonian than with the 

 Tropidoleptus fauna, which is distributed along the Appa- 

 lachian trough and as far around as into the Michigan embay- 

 ment, and (which is of much more interest) is also conspicuous 

 among the Devonian faunas of South America. 



Knowing then what are the characteristics of the Tropido- 

 leptus fauna in its typical region in North America, its pres- 

 ence may be recognized by the dominance of the dominant 

 species, or several of them associated together. By this test 

 we discover that, although the Productella speciosa fauna is 

 quite distinct from it and is known to follow, by several 

 hundred feet, the top of the Hamilton formation of Cayuga 

 Lake, its time-equivalence is with the later life period of the 

 Tropidoleptus fauna. 



This is shown by the fact that the faunules occurring at the 

 same horizon in the eastern part of the state maintain the bionic 

 equilibrium peculiar to the Tropidoleptus fauna ; and by the 

 second fact that above the typical Ithaca formation, in the 

 midst of the Spirifer disjunctus fauna, occur faunules in which 

 the dominant characteristics of the Tropidoleptus fauna are 

 still found associated with species not found either below in 

 the Hamilton formation of that meridian or in the Tropi- 

 doleptus fauna in its metropolis area. 



The details of these facts have been more fully elaborated by 

 Dr. E. M. Kindle since my own statements regarding the gen- 

 eral facts were stated. f 



In Dr. Kindle's list of the species of the Ithaca formation, 

 based upon the analysis of 54 faunules, not a single species of 

 the ten standard list species of the Tropidoleptus fauna appears 

 until we reach the thirteenth species in rank of the Ithaca list ; 

 and the second one is nineteenth in bionic rank in the Ithaca 

 list. This shows plainly that the Productella fauna is not 



* Proc. A. A. A. S*. xli p. 169. 



f Bull.' 3, U.S. Geo'l. Surv., 1884; Bull. 6, Am. Paleontology, 1896. 



