io6 



ROCHESTER ACADEMY OF SCIENCE. 



[Jan. 



A comparison of these columns shows that the new fauna 

 agrees with that of the Canadian Guelph in the following par- 

 ticulars : the absence of Echinoderms, the rarity of the trilobites, 

 and in the large proportion of Gasteropoda and Cephalopoda, really 

 a closer agreement in general characteristics than that of the Wiscon- 

 sin and Canadian Guelph faunas. 



It is not now deemed best to dwell upon the differences between 

 the new fauna and those represented in the remaining columns fur- 

 ther than to remark that that difference is greater than is shown by 

 the figures, the species of Gasteropoda from the new fauna are none 

 of them identical with those of the New York Niagara shale or of the 

 Niagara limestone, the same fact is true of the Cephalopoda and the 

 other classes excepting three species which are also found in the 

 Canadian Guelph fauna. 



Beginning with the Niagara shale and tracing the development 

 of this fauna through the Chicago and Racine groups to the Wiscon- 

 sin Guelph, and finally to the Canadian Guelph, there appears to 

 have been a gradual extinction of the Coelenterata, Bryozoa, Echino- 

 dermata, Brachiopoda and Trilobita, and a marked development of 

 the Cephalopoda and Gasteropoda, a fact which has an important 

 bearing upon the relations of the Chicago and Racine beds to the 

 other strata of the Niagara epoch and which the writer hopes to dis- 

 cuss in a subsequent paper. 



Of the species found here twenty-three have already been shown 

 to be identical with or very closely allied to Canadian Guelph species, 

 among these may be mentioned the following : 

 Murchisonia macrospira, 



" logani. 



Pleurotomaria Durhamensis. 

 " Galtensis. 



