106 Cincinnati Society of Natural Fiastory. 
away with it. The small parcel received by me had been fortu- 
ituously overlooked, or it, too, would have shared the fate of the 
rest. Mr. G. K. Greene, of Albany, Ind., who also washed for 
Bryozoa at the Falls, saved some of the fine residue. He kindly 
picked out some of the Ostracoda and sent them to me for examin- 
ation, but I found nothing among them not already known to me. 
In this manner I succeeded in gathering a large series of these 
small fossils, and the supply of the apparently new forms is not by 
any means exhausted with the present memoir. No; many 
remain unworked, while another paper, on Minnesota species 
mainly, is almost ready for publication. And yet, the tide has 
probably only just begun to set in. Nearly every locality affords 
one or more forms not before noticed. Most of the species so far 
known, including those of this paper, are from the Trenton, Cin- 
cinnati, Hamilton and Chester Groups, with very few from below 
the Trenton, and not many from the Clinton and Niagara, the 
latter the equivalent of the English Wenlock that has proven so 
prolific in Ostracoda. Nor does the number known from our Car- 
boniferous rocks at all compare with that described from European 
deposits of the same age. Here are numerous chances for the 
ambitious collector. 
Tne accompanying plates are reproduced from pen drawings by 
the photo engraving process. With the exception of Plate XI, 
on which the outlines were obtained by means of dividers and 
measurements, all were drawn with the aid of a camera-lucida. 
No effort was made to produce either artistic or mechanical tri- 
umphs, but in every essential respect the figures are reliable. 
The specimens used in the descriptions, belong in every case to 
the author’s cabinet. . 
The descriptions are grouped geologically, and under that zool- 
ogically as near as possible, into three parts as follows: 
Part I.—Lower Silurian Species. 
Part IJ.—Upper Silurian and Devonian Species. 
Part I1I.—Carboniferous Species. 
