NO. 2297. BRACHIOFOD GENUS FLATYSTROPHJA—McEWAN. 



399 



In the extensive collections belonging to the United States National 

 Museum no members of this genus were found below the Black 

 Eiver Group. Professor Cumings investigated this point and reached 

 the same conclusions. He says: ' 



I am unable to find any original references in the literature to its occurrence in 

 the rocks of tliia age (Chazy). Messrs. Ami, Whiteaves, and W. Billings of Ottawa, 

 Canada, inform me that the Museum of the Canadian Survey contains no Chazy speci- 

 mens; and that they are not aware that the species has ever been found in that series. 

 Mr. Billings suggests that it may have been found in rocks formerly held as Chazy. 

 but now known to be of later age. Mr. McBride, of Montreal, writes that there are 

 no Chazy specimens in the Museums at Montreal and that he does not know of the 

 occurrence of Platystrophia in the Chazy. Mr. Seely, who is familiar with the Chazy, 

 writes to the same effect. It is very probable, therefore, that the form is not known 

 to occur below the Trenton in this country. 



Wliile our knowledge does not substantiate the occurrence of this 

 genus below the Decorah Shale, the degi-ee of variation which it 

 has reached by that time leads the writer to expect that earlier 

 species will come to light with more extended investigation. 



The Black River and early Trenton species show but little varia- 

 tion in general physiognomy. The shells are equiconvex and have 



» Amer. Joum. Sci., ser. 4, vol. 15, 1903, p. 5. 



