164 THE CHICAGO ACADEMY OF SCIENCES. 



The writer is under very great obligation to Mr. Teller, not only 

 for the use of these specimens but also for the privilege, on 

 several occasions, of examining his collection, a privilege which 

 has rendered great assistance in the understanding of many of 

 the species from the localities in the Chicago area. 



The species described in this report are from several dis- 

 tinct horizons in. the Niagaran limestone, and do not constitute 

 a part of one compact fauna. The lowest horizon represented is 

 a brown limestone from near Channahon, Will County, Illinois, 

 near the Des Plaines river. The material from Joliet is higher, 

 that from Lemont still higher, and that from Hawthorn and 

 Bridgeport highest of all. The higher horizons are probably 

 nearly as young as the Guelph formation of Canada and New 

 York, while the lowermost may be as old as the Clinton in the 

 New York section. Accurate correlation of these beds can be 

 attempted, however, only when much additional detailed 

 stratigraphic work has been done throughout the area. 



A number of the species which have been recognized are 

 closely related to European forms. Among these may be men- 

 tioned Deiphon americanus, Staurocephalus obsoletus, Cerato- 

 cephala goniata, etc., and the presence of such forms in the 

 interior of North America, adds strength to the hypothesis of 

 communication between this region and northern Europe by 

 way of the north polar region, which was set forth in the "Geo- 

 logic Introduction" to part I. of this Bulletin. \ 



Since the publication of the "Geologic Introduction," how- 

 ever, it has been established that there were two quite distinct 

 faunal provinces in North America during Silurian time. One 

 of these was the great Mississippian province in which the 

 Chicago area lies, and it was this province that was in communi- 

 cation with north Europe during middle and later Niagaran 

 time. During the time preceding this northern communication, 

 while the Clinton beds were being deposited, it seems probable 

 this Mississippian province was not so extensive and that its 

 connection was with the Altantic basin, perhaps in some south- 

 easterly direction. 



During later Silurian time a quite distinct faunal province 

 occupied the northern Appalachian region. The sea in which 

 this Appalachian fauna flourished, occupied an. embayment from 

 the Atlantic which stretched northward from Maryland across 

 Pennsylvania and New Jersey into New York, which has been 

 called the Cumberland basin by Ulrich and Schuchert.* The 



*Rep. N. Y. State Paleontologist, for 1901, p. 647 (1902). 



