lO 
SMITHSONIAN INSTITUTION 
always made to scale upon a photographic basis, and are of natural size except 
as indicated in the legend. 
While the chief purpose of this treatise is to bring to light the new genera 
and species which have been discovered within the areas hereinbefore indicated, 
it is also hoped to increase our knowledge of forms previously known where new 
information has been gained by later discoveries. But where such species have 
already been adequately illustrated and described, they will not be included here. 
As to synon3miy. Dr. Bassler’s Bibliographic Index of Ordovician and 
Silurian Fossils, published by the United States National Museum as Bulletin 94, 
in 1915, brings references to all essential literature relative to American genera 
and species down to that date in the greatest detail and most convenient form. 
The publication has been widely distributed, and is available in every scientific 
library and in the hands of all working paleontologists. It is therefore unneces- 
sary to encumber these pages with the usual full citations of authors previous to 
that date, inasmuch as a simple reference to that work will alTord all the needful 
information. I am thus at liberty to limit my references covering dates previous 
to 1915 to such of the treatises as may for the sake of clarity or convenience be 
deemed of special importance in the history of the form under consideration. 
In the notation of Horizon and Locality in connection with species, I am 
avoiding the needless repetition of the term “ Silurian,” inasmuch as all species 
herein described, unless otherwise stated, are from that horizon, and reference 
to the respective formations is usually cjuite sufficient to identify the geological 
position. 
The material upon which this work is based is derived from the following- 
sources, consisting of collections either made for, or acquired by, myself, and 
now in the United States National IMuseum, and those belonging to other own- 
ers which I have been privileged to study : 
Author s Collections Used 
Rochester Shale; Lockport, New York 
By Frederick Braun, 1910, 1912, 1914. From Dr. E. N. S. Ringueberg, 
collection, Lockport. 
Osgood, Laurel and Waldron ; Indiana and Tennessee 
By Charles S. Beachler, 1887; St. Paul and Waldron. Braun, 1911; at 
St. Paul. Bassler and Braun, at Newsom, Tennessee. Llerrick E. Wilson, 1915, 
1916, 1917; St. Paul, Indiana. 
From Dr. Moses Elrod, collection; Flartsville, Indiana. Dr. C. C. Wash- 
burn; Waldron, Indiana. Mr. John E. Hammell, collection; Madison, Indiana, 
including that of A. C. Benedict; St. Paul and other southern localities and 
northern area. 
