60 CANADIAN MICRO-PALiEONTOLOGY. 



specimens in plate 10, in the first place interfered as to plates 

 10 and 11 ; and afterwards the acquisition of new material, 

 which had to be shown in plates 12 and 13, made it necessary to place 

 the species just as the convenience of figuring and the exigencies of 

 circumstances allowed. Nor could the highly desirable plan of having 

 a uniform scale throughout for magnifying the objects be adopted. The 

 descriptions have taken a long time ; but with this unavoidable delay 

 many opportunities have arisen for the widening of experience, the 

 collating of the results of other workers, and the forming of definite 

 opinions — such, for instance, as relates to the evidence of Cambro-Silurian 

 (Lower Silurian) forms being direct predecessors of Silurian 

 (Upper Silurian) species. Nor are such links wanting between these 

 Lower Palaeozoic and some Upper Palaeozoic species. 



There was at first considerable doubt as to the geological position of 

 Isochilina grandis, var. latimarginata and its associates ; but Mr. Tyrrell 

 informed me, in January last, that ''during the past summer a prac- 

 tically complete section has been obtained up the Saskatchewan Kiver, 

 showing that the Osti'acod-bearing series overlies several hundred feet 

 of Niagara Limestone, and on Lake Manitoba is overlain by a dolomite 

 containing a few fossils that have been provisionally referred to the 

 Guelph. The beds are also very similar in character to those in Wis- 

 consin that contain Leperditia alta, and that have been referred by 

 Prof. Chamberlin to the Lower Helderberg. 



The Ostracodal beds of Lake Winnepegosis, therefore, have a taxo- 

 nomic position somewhere between the upper beds of the Niagara and 

 the Lower Helderberg." 



Thus Isochilina gi-andis, var. latimarginata and the other Ostracods 

 occurring with it belong either to the top of the Niagara or to the 

 Lower Helderberg formation; both fossils and strata pointing in that 

 direction. 



The geological order of the localities from which the fossils herein 

 described have been obtained is as follows : — 



1. Black Island, Lake Winnipeg. Chazy. 



2. Nepean, Ontario. Chazy. 



3. Ottawa, Ontario. Chazy. 



4. Drill Shed, Quebec. Chazy ? [ Cambro- 



5. South of Montcalm Market, Quebec. Chazy ? 



6. Pointe-aux-Pins, Aylmer, Prov. of Quebec. Chazy. [ Silurian. 



7. Broad Street, Aylmer. Chazy. 



8. Gloucester, Carleton Co., Ontario. Birdseye or Black-river. 

 7. Lorette Falls, River St. Charles. Trenton. 



