GUELPH FAUNA IN THE STATE OF NEW YORK 135 



West of Lake Michigan these deposits spread over southern Wisconsin, 

 northern Illinois and into Iowa, where their extension in this direction is 

 terminated by the barrier of earlier formations. In Ohio it borders the 

 north and east shores of the Cincinnati dome. 



Over all this amphitheater, bounded without by the Niagaran, we may 

 conceive of a shallowing sea, dotted with coral banks which must in no 

 small measure have fringed the shore. Indeed contiguity to the shore line 

 of the Cincinnati dome is clearly indicated by the Hillsboro sandstone inter- 

 bedded with the upper dolomites. It was an almost inclosed sea, its open- 

 ing being probably through the narrow way toward the north and northwest, 

 a region which still holds the clue to many of our exotic faunas. 



In this connection it appears also significant that in the terminal beds 

 of the upper Siluric of Gothland a fauna appears which contains the genera 

 characteristic of the Guelph and often species which are hardly distinguish- 

 able. These are specially contained in the beds f, g, h ; f being character- 

 ized 1 as limestone beds composed of crinoids and corals ; g, large banks of 

 Megalomus and Trimerella, and h, Cephalopodan and Stromatopora beds. 

 In looking over these lists one can not fail to conceive the idea that the 

 much richer fauna of these beds contains a vicarious fauna of the American 

 Guelph, for we find there Monomerella, Trimerella (with three species), 

 with the absence of the majority of the Wenlock forms ; Megalomus among 

 the lamellibranchs ; Trematonotus and a very large number of cephalopods 

 and gastropods, including Pleurotomaria, Murchisonia, Loxonema, Trochus, 

 Pycnomphalus, Horiostoma, etc. ; also Stromatoporas. 



The appearance of such peculiarly adapted forms as the Trimerellas 

 and Megalomus, at corresponding horizons and in similar associations, is 

 certainly very suggestive not only of the presence of the identical facies, 

 but also of faunistic intercourse between the two seas. 



There is a generally recognized distinction between the rich Siluric 

 faunas of northern Europe and those of Bohemia and the Mediterranean 



' See Swedish State Mus. Pal. Dep't. ed. List of the Fossil Faunas of Sweden, II, Upper 

 Siluric. 



